Bell was absent when practice began Monday morning at the UPMC Rooney Sports Complex. He didn't show up for training camp and has not signed his $14.54 million franchise-tag tender.
In 2017, he didn't take part in offseason activities or training camp, his first year on the franchise tag. He didn't show up for practice until the Monday before the first game of the season. The Steelers open the 2018 season Sunday.
"We are disappointed Le'Veon Bell has not signed his franchise tender and rejoined his teammates," general manager Kevin Colbert said in a statement. "Coach (Mike) Tomlin and the coaching staff will continue to focus on preparing the players on our roster for our regular season opener on Sunday against the Cleveland Browns."
Darnold, who won the job over veteran Josh McCown, will become the youngest opening-day starting quarterback in NFL history at 21 years, 97 days when he takes the field for the Monday night contest against the Lions.
"We feel like he gives us a good chance to win," Bowles told reporters. "We're not starting him because he's a rookie and he's not ready. We're starting him because he gives us a good chance to win the game."
--Colin Kaepernick and Nike unveiled a new ad featuring the quarterback as part of the company's 30th anniversary "Just Do It" campaign.
The image, which Kaepernick tweeted out, shows a black-and-white closeup of the quarterback's face and the words, "Believe in something. Even it if it means sacrificing everything. Just do it."
According to ESPN, Nike has kept paying Kaepernick -- who signed with the brand in 2011 -- despite not using him in ads over the past two years, but planned to bring him back at the right time.
--Philadelphia Eagles coach Doug Pederson finally confirmed what everyone already knew: Nick Foles will start Thursday's season opener against the Atlanta Falcons.
Pederson made it official Monday when he addressed reporters in the auditorium at team headquarters, ending months of questions: "Nick Foles is the starter and we have complete confidence, obviously, in what he can do. We're ready to go with Nick."
The announcement follows a testy exchange Pederson had with reporters on Sunday when he was angry about a published report that said he had named Foles the starter. He said he never made such a declaration.
--Nathan Peterman, not first-round pick Josh Allen, was named starting quarterback of the Buffalo Bills.
Peterman, a fifth-round pick in 2017, threw five interceptions in his first NFL start against the Los Angeles Chargers last season when former Buffalo quarterback Tyrod Taylor briefly lost the job.
A stern test awaits Peterman, with the Baltimore Ravens, San Diego Chargers and Minnesota Vikings on the schedule the first three weeks of the season. Allen, the No. 7 pick in the 2018 draft, is the No. 2 quarterback for the Bills to open the season.
--Indianapolis Colts quarterback Andrew Luck returned to practice after taking a week off to recover from a minor foot injury.
He injured the foot Aug. 25 in a preseason game against the San Francisco 49ers. As long as Luck does not sustain another injury, he is on track to make his first start since the end of the 2016 season when the Colts meet the Cincinnati Bengals on Sunday.
Luck, who turns 29 on Sept. 12, missed all of last season while recovering from surgery to his throwing shoulder, but all indications are his shoulder won't be an issue when the season opens.
--Browns wide receiver Josh Gordon returned to practice and is expected to play in Sunday's regular-season opener against the Steelers.
The team's No. 3 wideout was slowed by a hamstring injury last week.
Coach Hue Jackson said Gordon, who was away from the team during training camp while in rehab at the University of Florida, would not start against Pittsburgh. Rookie fourth-round pick Antonio Callaway will start in Gordon's place, per Jackson.
--Bills running back LeSean McCoy will not be placed on the commissioner's exempt list and is eligible to play Sunday in the opener at Baltimore, the NFL said.
NFL spokesman Brian McCarthy told the Washington Post that the running back's status "has not changed" as police continue to investigate an alleged home invasion at McCoy's Milton, Ga., house, which happened in July.
Meanwhile, the Bills are bringing in former Denver Broncos quarterback Paxton Lynch for a visit Tuesday, according to an NFL Network report, and coach Sean McDermott named Ryan Groy the starting center over Russell Bodine.
--The Dallas Cowboys intend to keep center Travis Frederick on the active roster instead of sending him to injured reserve, according to multiple reports.
The plan means the team expects Frederick to return sooner than midway through the regular season. If he were placed on IR, he could not be recalled until after Week 8, though the team would have a free roster spot to use in the interim. If kept on the active roster, Frederick can return to play whenever he is healthy.
No timetable has been given for Frederick's return since he was diagnosed with Guillain-Barre syndrome two weeks ago, after he saw several specialists to determine the cause of repeated stinger-like symptoms experienced during training camp.
--New York Giants coach Pat Shurmur expanded on the decision to waive quarterback Davis Webb to make room for other players claimed on waivers Sunday.
"I think I mentioned long ago there was no depth chart behind Eli (Manning)," Shurmur told reporters. "(Webb) got a lot of reps, and I think it was probably that where people start to assume because he's taking second-string reps that he's a second-string quarterback, and it didn't play out that way."
Meanwhile, tight end Evan Engram practiced on a limited bases but remains in the concussion protocol, and defensive end Olivier Vernon missed practice as he recovers from an ankle injury. Shurmur said the team is hopeful both players can play Sunday against the Jacksonville Jaguars.
--The Denver Broncos will start rookie third-rounder Royce Freeman at running back, coach Vance Joseph told reporters.
Freeman will be the first rookie to be the Broncos' Week 1 starting running back since Terrell Davis in 1995. He and third-year veteran Devontae Booker shared first-team reps throughout training camp and the preseason, but the rookie shined in preseason games with 15 carries for 84 yards and three touchdowns.
Joseph has been vocal about the team's plan to use multiple backs throughout the season. He reiterated Monday that Freeman will handle the bulk of early-down work, while Booker is likely to take the lead in passing situations.
--Tennessee Titans tight end Delanie Walker and outside linebacker Brian Orakpo said they will be ready for Sunday's season opener against the Dolphins in Miami, while right tackle Jack Conklin is getting closer to a return.
Walker, who has been battling an apparent toe injury, and Orakpo (shoulder) each returned to practice last week after missing all of the preseason. The Titans have been extremely tight-lipped about injuries under new head coach Mike Vrabel, but both players expect to play.
Conklin, who tore the anterior cruciate ligament in his left knee in the divisional playoffs in mid-January, was activated from the physically unable to perform list before final cuts and did limited work in individual drills at Monday's practice. General manager Jon Robinson said Conklin is "progressing nicely," but no timetable has been given for the tackle's return.
--Starting left tackle Donovan Smith and rookie first-round defensive tackle Vita Vea both missed practice as the Tampa Bay Buccaneers prepared for Sunday's game at the New Orleans Saints.
Smith sprained his right knee two weeks ago in practice and was given a timetable of two to four weeks to return. Vea, drafted 12th overall in April, has missed more than a month with a strained calf muscle, which initially was not expected to cost him regular-season games.
The Bucs also announced four roster moves, claiming defensive end Carl Nassib off waivers from the Cleveland Browns, placing defensive tackle Mitch Unrein on injured reserve, releasing defensive end Will Clarke and re-signing long snapper Garrison Sanborn.
--The Detroit Lions and safety Quandre Diggs agreed to a contract extension that runs through the 2021 season, the team announced.
Terms were not announced, but the Detroit Free Press pegged the deal at $20.4 million.
Late last season, Diggs moved from slot cornerback to safety after Tavon Wilson sustained a torn biceps. In five starts, he had three interceptions and a forced fumble. Diggs is expected to pair with Glover Quin at safety for the Lions.
--The 49ers officially placed running back Jerick McKinnon on injured reserve, two days after he tore the anterior cruciate ligament in his right knee during a non-contract drill in practice.
McKinnon, 26, played four seasons with the Vikings before signing a four-year, $30 million deal with the 49ers in the offseason. He rushed for a career-best 570 yards last season.
San Francisco also announced it signed offensive lineman Matt Tobin and safety Antone Exum Jr. to one-year contracts, placed safety Marcell Harris on injured reserve and signed offensive lineman Zack Golditch to the practice squad.
--The Oakland Raiders signed veteran wide receiver Brandon LaFell and released wideout Johnny Holton, the team announced.
LaFell, 31, was released by the Bengals in early August after two years with the team. He will serve as another veteran target after the Raiders released Martavis Bryant -- acquired for a third-round pick in April -- during final cutdowns.
The Raiders also announced they claimed defensive tackle Brian Price off waivers from the Cowboys and waived defensive tackle Treyvon Hester.
--Quarterback Christian Hackenberg was signed to the Bengals' practice squad, the club announced.
The former second-round pick will be joining his fourth organization of the year.
Hackenberg spent his first two seasons with the Jets and didn't get into any games. He was traded to the Raiders in May for a conditional seventh-round draft choice and later was waived. The Eagles signed him last month and released him on Friday.
--The Browns are considering starting undrafted rookie Desmond Harrison at left tackle in their season opener.
The 6-foot-6, 295-pound Harrison played at Texas and later transferred to West Georgia. He could make history by replacing 10-time Pro Bowler Joe Thomas, who retired in March.
If Harrison does not start, veteran Joel Bitonio could anchor the line at left tackle. Bitonio also is a possibility to start at guard.
--Chicago Bears pass rusher Leonard Floyd returned to practice wearing a club on his broken right hand. He sustained the injury Aug. 18 in a preseason game against the Broncos but is expected to be ready for Sunday's season opener at Green Bay.
--The Cowboys re-signed wide receiver Deonte Thompson and placed fellow wideout Noah Brown on injured reserve because of a hamstring injury. Thompson provides depth at a position that includes Terrance Williams, Allen Hurns and Cole Beasley.
--The Lions signed linebacker Marquis Flowers, a former member of the Patriots who will reunite with coach Matt Patricia. Detroit scooped up Flowers less than 48 hours after New England let him go.
--The Miami Dolphins signed center Travis Swanson three days after he was released by the Jets. Swanson figures to serve as a backup for Daniel Kilgore, who is set to replace Mike Pouncey in South Florida.
--The Green Bay Packers signed veteran linebacker Korey Toomer, who was cut by the 49ers over the weekend. The 29-year-old Toomer has appeared in 46 games (16 starts) in parts of five seasons with Dallas, St. Louis, Oakland, San Diego-Los Angeles and San Francisco.
--The Kansas City Chiefs claimed center Austin Reiter off waivers from the Browns and released Bryan Witzmann, who made 13 starts in 2017.
--Field Level Media