Martin has not played since Week 7 of last season, when he accused his Dolphins teammates of bullying him and left the team. Richie Incognito was at the center of the scandal and was suspended indefinitely by the Dolphins while the NFL investigated Martin's claims.
In February, independent investigator Ted Wells issued a report outlining the details of the bullying case.
The NFL reportedly cleared Incognito for a possible comeback, but he remains unsigned.
Martin was a second-round pick in 2012. The 49ers acquired him for a conditional seventh-round draft pick in March.
Martin played college football for Stanford under current 49ers head coach Jim Harbaugh.
- Dan Gartland