San Francisco 49ers head coach Kyle Shanahan announced Wednesday that Brock Purdy has entered the NFL's concussion protocol, putting the team's starting quarterback's status for Sunday's game against the Cincinnati Bengals in question.

Shanahan said Purdy began to experience symptoms on the team's flight home from Monday's game against the Minnesota Vikings. The second-year pro played every snap of the 49ers' 22-17 loss.

"We found that out when we landed, we were all pretty asleep," Shanahan told reporters. "He got all checked up (Tuesday) and now he's in the protocol."

Veteran Sam Darnold ran the first-team offence in Wednesday's practice and would start Sunday if Purdy doesn't receive medical clearance. Shanahan said Purdy's availability will be determined later in the week.

"He does have enough time [to clear protocol], he just has to go through the process," Shanahan said.

With Brock Purdy in concussion protocol, 49ers’ QB Sam Darnold now is in line to start Sunday’s game vs. the Bengals. pic.twitter.com/NNigQ9XEy4

— Adam Schefter (@AdamSchefter) October 25, 2023

Purdy, the 262nd and final pick of the 2022 draft, won his first 10 NFL regular-season starts dating back to his rookie year, but has lost his last two and struggled in both games. The 23-year-old completed just 12 of 27 passes for 125 yards in San Francisco's 19-17 loss at Cleveland in Week 6, then was intercepted twice against Minnesota.

The Iowa State product posted a 123.1 passer rating with nine touchdowns and no interceptions over the course of the 49ers' 5-0 start to this season.

Darnold started six games for the Carolina Panthers last season and went 4-2 in those games while throwing for 1,143 yards with seven touchdowns and three interceptions. The 2018 No. 3 overall draft pick signed a one-year contract with the 49ers in March and won the No. 2 quarterback job from another former No. 3 overall pick, Trey Lance, during the preseason.

The 49ers subsequently traded Lance to the Dallas Cowboys shortly before the start of the season.