San Francisco 49ers quarterback Brock Purdy is in concussion protocol, putting his status for this week's game against the Cincinnati Bengals in doubt.

Coach Kyle Shanahan said that Purdy reported symptoms on the flight home after Monday night's loss in Minnesota and was placed in the protocol.

Purdy is feeling better Wednesday and will be able to take part in a portion of San Francisco's walkthrough practice but still must clear several protocols in order to play on Sunday against Cincinnati.

“He definitely has enough time," Shanahan said. “He just has to go through the process.”

Shanahan said Purdy could play without practicing this week if he clears the concussion protocol, pointing to his performance in a Thursday night game last season against Seattle when he didn't practice because of injured ribs.

Shanahan said he was uncertain when Purdy took the hit that led to the concussion, but said it might have happened on a quarterback sneak attempt midway through the fourth quarter. He said he didn't see any signs on film that Purdy was hampered by it down the stretch but he did throw interceptions on his final two drives of the 22-17 loss.

If Purdy can't go on Sunday, the Niners will turn to Sam Darnold, the the 2018 No. 3 overall pick who signed with San Francisco as the backup this season.

Darnold struggled for his first five seasons with the New York Jets and Carolina before signing this offseason with San Francisco. He beat out the 49ers' 2021 No. 3 overall pick Trey Lance for the backup job.

“I have as much confidence in Sam as I could with someone I haven't gotten into a real NFL game with,” Shanahan said. “He was great in the offseason and great in these seven weeks so far. He's always ready go.”

Darnold has started 55 games in his career. His 78.2 passer rating is the worst among 38 quarterbacks who have thrown at least 1,000 passes since he entered the league in 2018. But Darnold has never had as talented a team to work with as he has in San Francisco.

The 49ers were impressed with Darnold's work in the offseason and preseason and said that has carried over into his role as scout team quarterback.

“He's accurate, a decisive thrower, good with his reads and everything," cornerback Charvarius Ward said. "I think if we need him this week, I expect him to go out there and put up some points.”

NOTES: LT Trent Williams (ankle) didn't practice but could be back on the field Thursday after missing last week's game. ... LB Dre Greenlaw got a rest day and WR Deebo Samuel (shoulder) remains sidelined. ... Shanahan said defensive coordinator Steve Wilks lost track of time when he called for a blitz with 16 seconds left in the first half. The Vikings scored a 60-yard TD on the play. “He knows he messed up on that call,” Shanahan said.

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