Martin, 25, was selected by the Dolphins in the second round of the 2012 NFL draft. He stayed with Miami for two years before being traded to the 49ers. He was claimed by the Carolina Panthers this off-season after the 49ers cut him.
Martin started all 16 games for the Dolphins in 2012. He started seven games in 2013 before accusing teammate Richie Incognito of bullying him, which prompted an investigation into the Dolphins' locker room culture and resulted in an eight-game suspension for Incognito.
Last season, Martin started nine games for the 49ers, who finished third in the NFC West with an 8-8 record.
- Erin Flynn