Amir Khan was found in tears in his dressing room after losing against Terence Crawford with the WBO welterweight title at stake.
The two-weight world champion was left unable to continue after a low blow by Bud in the sixth round, with trainer Virgul Hunter pulling him out.
Khan was floored in the opening round by the undefeated American, and was behind on all of the judges scorecards before the bizarre ending at Madison Square Garden.
The 32-year-old has now lost five fights in his professional career, with four of those defeats coming by knockout.
And after he failed in his attempt to win a world title for the first time since 2012, the 2004 Olympic silver medallist was spotted in tears by BT Sport cameras who were allowed backstage.
Many boxing fans have tweeted that Khan quit to spare himself from further punishment – with rival Kell Brook stating he was “looking for a way out”.
While Crawford was also of the opinion that Khan quit as he urged him to “tell the truth” as he laughed off his claims that the low blow had a serious impact.
Khan vehemently denied the accusations labelling him as a quitter, saying: “I was caught with a shot right below the belt and I could feel it.