Schiano acknowledged it would be a stretch to expect Martin to play in Thursday night's game against the Carolina Panthers, but he wouldn't rule anything out beyond that.
A league source told ESPN NFL Insider Adam Schefter that the Bucs believed Martin suffered a torn labrum in his shoulder, an injury that could end his season.
But Schiano would not go into detail about the exact nature of the running back's injury.
"I'm not going to get into specifics of exactly what his issue is," Schiano said. "If it was season-ending, I'd let you know. But we don't feel that it is right now. We're just going to play it by ear."
Martin suffered the injury in Sunday's loss to Atlanta while attempting to catch a pass in the third quarter. Martin said after the game that X-rays "look fine" and that his shoulder was not separated.
The 24-year-old Martin had been scheduled to undergo an MRI on Monday, a source said.
Rookie Mike James took over for Martin against the Falcons and would be the likely starter against Carolina.
"I've liked what I've seen of Mike the last few weeks, both in practice and the game," Schiano said. "He's gotten a few more touches each game and obviously this one by necessity.
"I think Mike has really improved as a running back from the beginning stages of training camp and made improvement steadily. When he's had his opportunities, he's done good things."
One of the NFL's top rookies last season, Martin was off to a slow start this year for the winless Buccaneers (0-6). He has 456 yards on 127 carries -- an average of just 3.6 yards per attempt -- and one touchdown.