Mullens has been on the 49ers roster as a backup to C.J. Beathard since Jimmy Garoppolo went down with a torn ACL, but he has not appeared in any regular-season games.
Adam Schefter of ESPN reported Mullens will start against Oakland because Beathard is bothered by a wrist injury that affects his ability to grip the ball.
Beathard will be in uniform and will serve as the backup quarterback. The 49ers waived No. 3 quarterback Tom Tom Savage earlier on Thursday.
Mullens was undrafted in 2017 after making 41 starts at Southern Miss. He was signed to the 49ers’ practice squad last year and had been on the practice squad until Garoppolo suffered his injury.
During the 2018 preseason, Mullens went 31 of 43 for 396 yards, one passing touchdown, two rushing touchdowns, three interceptions, and two lost fumbles.
Beathard became the starting quarterback after Garoppolo was lost for the season with a knee injury. But Beathard has been out of practice this week with the wrist injury.
Savage was the only other quarterback on the 49ers’ roster and he was waived on Thursday. He played for the Houston Texans last season, and went 1-6 as a starter, while throwing five touchdown passes and six interceptions for the 2017 season.
The 49ers are 0-5 with Beathard as their starter this season and 1-9 over two seasons. He has completed 60.4 percent pf his passes this season with eight touchdown passes and seven interceptions.