San Francisco 49ers quarterback Brock Purdy has not yet cleared concussion protocol, but there is still a realistic chance he will start Sunday against the Cincinnati Bengals.

Purdy went into concussion protocol early Tuesday after feeling symptoms on the team's plane ride home from Minnesota late Monday night. Since then, Purdy has passed four of the league's five steps in the concussion protocol.

That has allowed Purdy to participate in practice on a limited basis Thursday and then be full go in Friday's session.