Denver Broncos center Dan Koppen, who started 12 games last season, suffered a torn anterior cruciate ligament in his left knee and is out for the season, multiple media outlets reported.
Koppen was injured when he got caught in a pile up during a workout. He was carted off the field.
Koppen, 33, signed with the Broncos last month after J.D. Walton had a setback while recovering from a dislocated ankle. Walton could be back by mid-October, but any further complication could put him out for the entire season.
The Broncos now have Manny Ramirez, who is a guard, playing center and snapping the ball to Peyton Manning.
However, the Broncos announced they have agreed to terms with free-agent center Steve Vallos, pending his physical.
Vallos is a sixth-year player who has seen action in 44 career regular-season games, including nine starts.
---Pittsburgh Steelers offensive tackle Mike Adams is set to return after recovering from a stabbing in June, ESPN reported.
The second-year player was injured outside a Pittsburgh restaurant last month in an attempted carjacking. He underwent surgery for wounds to his abdomen and left forearm. His core strength has returned and he weighed in at 323 pounds, according to ESPN.
---Guard Jonathan Cooper, the seventh overall pick in this year's NFL Draft, agreed to a four-year contract with the Arizona Cardinals, the team announced.
The fully guaranteed contract is worth $14.55 million and includes payments of $3.4 million within 10 days, $3 million by Sept. 15 and $2.56 million by Oct. 15. ESPN reported. According to CBSSports.com, Cooper's contract structure is similar to No. 1 overall pick Eric Fisher of the Kansas City Chiefs and includes a more attractive signing bonus structure.
---Minnesota Vikings coach Leslie Frazier wants his team to focus on football, and asked wide receiver Greg Jennings to stop his public criticism of Green Bay Packers quarterback Aaron Rodgers.
Jennings was the Vikings' prized free agent pickup over the offseason after spending seven seasons with the Packers.
He has taken several verbal shots at Rodgers since signing with the Vikings, including saying he preferred playing with Brett Favre over Rodgers.
---The San Diego Chargers announced linebacker Jonas Mouton will be placed on injured reserve after clearing waivers. Mouton tore his anterior cruciate ligament during the first day of training camp Thursday and will miss the 2013 season.
---With Dennis Pitta expected to miss the entire 2013 season with a hip injury suffered Saturday during practice, the Baltimore Ravens added veteran tight end Visanthe Shiancoe to their roster.
The Ravens announced that Shiancoe agreed to a one-year contract. Shiancoe, 33, is a 10-year veteran who played in four games for the New England Patriots last season without making a catch.
---New York Giants safety Will Hill revealed the four-game suspension announced last week was for marijuana use to alleviate off-field stress last season.
Hill, who was suspended four games for Adderall use last season, said he has not used any banned substances this year and underwent drug rehabilitation this spring in Boston and continues to have outpatient meetings.
---Mark Sanchez opened the New York Jets' training camp practicing with the first team on Friday, but head coach Rex Ryan said second-round pick Geno Smith will get plenty of opportunity to get repetitions with the starters as the competition for the starting job heats up.
Ryan also said Smith has been working on zone-read formations in which the mobile rookie looked comfortable, although he has yet to work in live tackling situations.
---Donovan McNabb announced his intention to retire from the NFL in May, but he will make it official as a member of the Philadelphia Eagles on Monday, the team announced Sunday.
A retirement news conference is scheduled at 10 a.m. ET Monday at the team's training facility.