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.