Fox Sports had earlier reported the feared severity of Martin's injury.
Martin will have an MRI on his shoulder Monday and is unlikely to play Thursday against the Carolina Panthers, a source said.
Martin said after the game that X-rays "look fine'' and his shoulder was not separated.
"We're still evaluating what it is,'' Martin said Sunday, adding that he wasn't "sure yet'' if he would play in Thursday night's game.
"Just have to hope for the best.''
Martin suffered the injury while attempting to catch a pass in the third quarter. Rookie Mike James replaced Martin and finished with 14 carries for 45 yards.
One of the NFL's top rookies last season, Martin was off to a slow start this year for the winless Buccaneers (0-6). The 24-year-old rushed for 47 yards Sunday on 11 carries.
ESPN NFL Insider Adam Schefter and ESPN.com Buccaneers reporter Pat Yasinskas contributed to this report.