Sam Darnold won’t be getting his chance at redemption, after all.

The 49ers’ backup quarterback was in line to start on Sunday against the Bengals as starter Brock Purdy dealt with a concussion.

But Purdy quickly progressed through the protocol, passing four of the NFL’s five required steps before returning to game action during the week, and passed the final step on Saturday.

He was able to practice as a limited participant on Thursday and fully on Friday as a result, and now is set to be available to start on Sunday.

“That’s the last thing he’s got to do,” head coach Kyle Shanahan told reporters on Friday about the last step of the protocol. “Just one step left … He was full go today; he’s just got to pass that tomorrow.”

Purdy was officially listed as questionable on Friday, and Shanahan said he will “definitely” start if he cleared the protocol.

Purdy no longer has any injury designation.

He appeared to suffer the concussion while attempting a quarterback sneak during the team’s Week 7 loss to the Vikings.

He finished the game without exiting, though he threw two interceptions after that play.

He felt symptoms on the plane ride home Monday night and entered the concussion protocol on Tuesday.

Darnold is in his first season with the 49ers after signing a one-year, $4.5 million deal this past offseason, though it can rise as high as $11.5 million with incentives.

Formerly the No. 3-pick in the 2018 NFL Draft by the Jets, Darnold failed to live up to expectations across three seasons with the team.

He then played two seasons with the Panthers, starting 17 games.

It appeared he would get another chance to prove his worth as a starting quarterback, but Purdy’s recovery has thrown a wrench into that plan.

“He’s been great, as he normally is,” Darnold said of Purdy. “He’s preparing really well and out there at practice he’s been slinging it and looking really good.”