Pound-for-pound king Floyd Mayweather said he dislocated his left elbow in the middle of his majority decision over previously unbeaten Saul Alvarez.
The 36-year-old Mayweather earned a record $41 million purse Saturday for a dominating 12-round victory in which he claimed Alvarez's World Boxing Council and World Boxing Association super welterweight belts.
"I could have used more combinations down the stretch. I think I dislocated my elbow," said Mayweather during the post-fight news conference.
Mayweather said that for rounds six and seven he couldn't use his jab because of the suspected dislocated elbow, although round seven still turned out to be one of his strongest of the fight.
"My arm was hurting, and I wanted to stop using my jab and just paw with it," Mayweather said.
Doctors were expected to examine the elbow this week.
He used his superior hand speed to keep Alvarez at bay, but Mayweather still only managed to win the fight on two of the three judge's scorecards.
Judge CJ Ross surprisingly scored it a draw, 114-114. The other two judges, Craig Metcalfe (117-111) and Dave Moretti (116-112) had Mayweather winning in a breeze.
Ross surprised many by giving six rounds to Alvarez. She is also one of two judges who scored a win for Timothy Bradley over Manny Pacquiao last year.
Mayweather criticized Ross after the fight.
"I think it is a woman, and she could be older," said Mayweather.
Mayweather was fighting for just the second time since being released from prison after serving a sentence for assaulting the mother of his children.
Mayweather gave away 13 years in age and 15 pounds to the younger and stronger Alvarez.
The Mexican fighter tipped the scales at Friday's weigh in right on the 152-pound catch weight. But by the time he entered the ring, Alvarez had ballooned to 165, 13 pounds heavier than he was at the weigh in. It was also 10 pounds heavier than the weight he had been sparring at in the week leading up to the fight.
The added weight made him look slow and awkward in the ring as he suffered the first loss of his career.
This was the second fight in Mayweather's six-bout, 30-month contract with Showtime that could pay him more than $200 million.
Saturday's fight marked the first time since 2007 that he has fought twice in a calendar year, and Mayweather said he plans to repeat that schedule in 2014 and 2015 by fighting in May and September.
Mayweather repeated several times after the fight that he is counting down the months until retirement, and he believes he will stop boxing sometime in 2015.
"I only got 24 months left," he said.