Martinez was elevated from the 49ers' practice squad to the active roster Saturday.
Martinez signed with the 49ers' practice squad after failing to make the Jets' 53-man roster in late August. Brock Purdy (shoulder) and Kurtis Rourke (knee) are both expected to miss San Francisco's Week 2 matchup against the Saints, so Martinez's signing ensures depth at quarterback. He's expected to back up Mac Jones on Sunday.