Allen is a go for Sunday's contest in Orchard Park, N.Y., while Darnold is expected to be cleared prior to kickoff as the Jets (3-9) aim to snap a six-game losing streak when they visit the Bills (4-8).
Darnold has missed the past three games with a right foot injury but optimism over his return increased when he was a full practice participant on Wednesday for the first time since being injured against the Miami Dolphins in Week 9.
"I'm really excited about how I felt," Darnold told reporters, "so as of right now I'm really excited about hopefully getting a chance to play on Sunday."
Darnold, the No. 3 overall pick of this year's draft, has passed for 1,934 yards and 11 touchdowns but also has a low completion rate of 55 percent and an NFL-worst 14 interceptions.
Allen, the No. 7 selection, missed the first meeting due to an elbow injury that sidelined him four games. He has passed for 1,223 yards and five touchdowns against seven interceptions with a league-low 52.9 percent completion rate.
Allen suddenly has become a threat as a runner with back-to-back outings of 99 and 135 yards. He passed for two touchdowns for the first time as well in last week's 21-17 loss to the Miami Dolphins.
"I've done a really good job on protecting myself, whether it's getting down, sliding, or getting out of bounds," Allen told reporters of his running. "Obviously, sometimes hits are going to happen. That's football, whether it's in the pocket or outside the pocket.
"But I definitely don't want to be the leading rusher."
The loss to Miami halted a modest two-game winning streak for the Bills that began with a 41-10 rout of the Jets.
Barkley passed for 232 yards and two touchdowns and LeSean McCoy rushed for 113 yards for the lone time he has topped 100 this season.
The Buffalo defense intercepted McCown twice and limited him to 135 yards. That performance is one of four straight games in which the Bills have allowed 130 or fewer net passing yards, the first time an NFL team had done that since the New York Giants in 2009.
Buffalo leads the NFL in pass defense at 187.2 yards per game and ranks second in total defense at 294.2.
Those fine marks have been needed with the Bills struggling on the offensive end. The Bills rank 31st in both scoring offense (14.8 points per game) and total offense (285.7).
New York's offense also is near the bottom of the league in both categories, ranking 30th in total offense (301.0) and 26th in scoring offense (20.3).
The Jets failed to score an offensive touchdown in last week's 26-22 loss to the Tennessee Titans. New York built a 16-0 advantage before wilting in a performance that left coach Todd Bowles fuming.
"It's one of those games you'll remember for the rest of your life as a player or a coach. You'll never forget about it," Bowles told reporters. "It can propel you to be better at your job or it can make you go in a shell.
"I don't think we have those kinds of guys, but of course everybody is frustrated and (ticked) off."
While Bowles' employment status gets shakier by each defeat, Buffalo cut its losses by releasing receiver Kelvin Benjamin, a former 1,000-yard receiver with the Carolina Panthers who caught just 39 passes for 571 yards and two touchdowns in 18 games with the Bills.
"It obviously didn't work," Buffalo coach Sean McDermott told reporters of the acquisition made during the 2017 season. "The important thing for us is that we continue to take swings. Some of those are going to work and some of those aren't. The only way you can get a hit is if you take a swing."
Also, New York linebacker Darron Lee (74 tackles, three interceptions) will miss the contest after being suspended without pay for the final four games of the season due to a violation of the NFL's substance-abuse policy.
--Field Level Media