Martin is sitting out for "precautionary reasons," the source said, and the injury is not expected to affect him beyond this week.
The injury absence was first reported by The Tampa Bay Times and confirmed by ESPN.
Martin was a full participant in joint practices in Jacksonville, including Wednesday's padded practice. It is unclear when he suffered the injury.
As the primary running back in Tampa Bay's run-first offense, Martin totaled 1,402 yards -- second in the NFL -- on 288 carries with 6 touchdowns in 2015. He also had 33 receptions for 271 yards and 1 touchdown.