Bills coach Sean McDermott announced the move on Wednesday. Anderson is playing in place of rookie Josh Allen, who is dealing with an elbow strain. There is no plan for surgery, but Allen is now week-to-week. Allen suffered the injury in Sunday's 20-13 loss to the Houston Texans.
"It's football," Anderson told reporters. "Things that happen in this game never amaze me. You've gotta be ready at all times. I was fully aware of what I was getting myself into coming here. Obviously not ideal, but we are going to do what we can."
Anderson, 35, hasn't started an NFL game since the 2016 season with the Carolina Panthers. He owns a career passer rating of 71.1 with 10,413 yards, 60 touchdowns and 60 interceptions, while completing 54.1 percent of his throws. The 13-year veteran was a sixth-round pick by the Baltimore Ravens in 2005 NFL Draft.
"I was very optimistic of what had happened during the game," Allen said. "I had my dad and brother call me saying they saw different reports. People want to make all of these outside accusations and claims. But I'm trusting the doctors we've talked to and trust what we've seen."
"I'm relieved and happy it is what it is. I kinda get to step back and see D.A. from a different lens. See how he controls the huddle, how he operates. I'm looking at it as a blessing in disguise right now."
Anderson signed with the Bills last week after spending seven seasons with the Panthers. McDermott was the Panthers' defensive coordinator for six of those seasons.
The veteran gunslinger earned the start over Nathan Peterman, who was a fifth-round pick by the Bills in the 2017 NFL Draft. Peterman completed 49 percent of his passes last season for 252 yards, two scores and five interceptions in four games. He completed 6-of-12 passes for 61 yards, a touchdown and two interceptions in Week 6 for the Bills.
Allen, 22, was the No. 7 overall pick in the 2018 NFL Draft. The Wyoming product has completed 54 percent of his throws for 832 yards, two touchdowns and five interceptions on the season.