The Keith Thurman comeback has been put on hold -- the boxing star suffered a bicep injury that is forcing him to back out of his upcoming fight against Tim Tszyu.
The Boxing Voice broke the news of the ailment on Monday ... saying the 30-1 welterweight fighter was getting an MRI for a possible arm injury that could put his March 30 bout against Tszyu in jeopardy.
The fight is still a go ... but without Thurman -- ESPN Ringside's Mike Coppinger reported Tszyu will now defend his WBO junior middleweight title against Sebastian Fundora (20-1) instead.
This is unfortunate news for Thurman, who would've stepped in the ring for the first time in over two years ... and he previously said it was a chance to prove he's not washed.
"I believe boxing needs Keith Thurman. I really deliver some of the greatest entertainment on that world-class scene every time they put me in the ring," Thurman told us earlier this month.
"My haters are my real motivators!" So keep hatin' baby, and I'ma keep pushing."
Thurman also told us he was gunnin' for a knockout ... and his win against Tszyu would've been an opportunity to get closer to a match with Terence Crawford.
Thurman hasn't spoken about what this means for his career ... but like he told us -- he believes boxing needs him, so chances are he'll be back.