The 49ers signed Martinez from the practice squad to the active roster ahead of Thursday's game against the Rams.
Martinez was elevated from the 49ers' practice squad to the active roster for Week 2 and 3 to serve as Mac Jones' backup in the absence of Brock Purdy (toe). Purdy returned for Week 4 against the Jaguars but has been ruled out for Thursday's game in Los Angeles, so Martinez will once again be the QB2 while Jones makes his third start of the regular season.