Johnson was signed a day after coach Rex Ryan said Taylor was "beat up" and "sore" following a 14-13 win against Tennessee. Ryan then didn't go into specifics when asked whether Taylor might be too sore to play Sunday, when Buffalo (3-2) hosts Cincinnati (5-0).
"We all know he finished the game, but we'll see how he's doing," Ryan had said Monday. "We'll be looking at him throughout the week. ... But he's sore now, I can tell you that much."
Ryan is next scheduled to speak with reporters on Wednesday. Taylor was not spotted in the Bills locker room during a 45-minute period when players are available to reporters on Tuesday.
Taylor was sacked four times and took several big open-field hits while nearly single-handedly rallying the Bills to score two touchdowns in the final 16 1/2 minutes. He finished with a team-best 76 yards rushing, including a 22-yard touchdown, and completed 10 of 17 attempts for 109 yards and a touchdown.
Taylor finished the game despite leaving for one play in the fourth quarter after turning his left ankle while being tackled following a 24-yard run.
Ryan also revealed Monday that Taylor has been bothered by a nagging ankle injury since training camp. Ryan didn't say when or which ankle Taylor hurt.
Johnson adds experienced depth behind Taylor and backup EJ Manuel, the Bills former starter who lost his job a month into last season.
In six NFL seasons, Johnson has 1,042 yards passing, five touchdowns and 10 interceptions in 29 games, including five starts. He was signed a day after being cut by Indianapolis, and has also played for Tampa Bay, Cleveland, Cincinnati and San Francisco.
The Bills turned to Johnson after first expressing interest in signing Matt Simms off the Atlanta Falcons practice squad, two people familiar with the discussions told The Associated Press. Simms, however, elected to stay in Atlanta, the two people said speaking on the condition of anonymity because the Bills did not disclose that information.
Simms is familiar with the Bills offense after spending the preseason in Buffalo before being cut on Sept. 4.
To make room on their roster, the Bills cut kicker Billy Cundiff a week after signing him. Cundiff replaced Jordan Gay as the team's kickoff specialist, while veteran Dan Carpenter handled field-goal and extra-point duties.