Mullens is expected to undergo surgery after sustaining a right elbow surgery in Sunday's 41-33 loss to the Cowboys, Matt Maiocco of NBC Sports Bay Area reports.
Mullens isn't expected to be available for Saturday's game against the Cardinals, and he would almost certainly be done for the season if he undergoes surgery. Moving forward, C.J. Beathard is in line to be the 49ers' starting quarterback in Week 16, although Jimmy Garoppolo (ankle) will return to practice this week and is eligible to play Saturday. If Mullens' season is over, he'll finish with 2,437 passing yards, 12 touchdowns and 12 interceptions.