Butler, a second half sub at Wolves on Tuesday will definitely be out for the weekend trip but should be back for the Watford game on Sunday week with Roberto not ready to take chances on an injury at this stage of the season.
Speaking to Wales Online, the Swans boss said “We had bad news with Tom on Wednesday
“He felt his hamstring slightly and he will be missing against Doncaster.
“We can’t take any risks with that sort of injury. It’s nothing serious or long-term though and he should be available for the Watford game”
Martinez also said that despite their first defeat in six on Tuesday, confidence in the camp remained high
“Confidence hasn’t been affected at all,” he said.
“I think we can take a lot out of that performance.
“If I had to lose again it would be the way we did against Wolves.
“The way we passed the ball, kept control and defended all over the pitch was very impressive for a team that has only just been promoted.
“Doncaster will be a completely different kind of challenge and it will be a difficult place to go at this time.
“It’s going to be scrappy because they are fighting for every point.”