Eddie Hearn, promoter for Callum Smith, believes his boxer suffered a bicep injury in the early rounds of his twelve round fight with Mexican superstar Saul "Canelo" Alvarez.
Smith was battered over twelve rounds, as Canelo powered his way to a lopsided unanimous decision win at the Alamodome in San Antonio, Texas.
With the win, Canelo walked away with the WBC, WBA super middleweight titles.
Smith, who suffered his first defeat as a pro, took a lot of punishment to the head and body - especially in the second half of the contest. It got to the point where some observers felt the contest had become too one-sided and should have been stopped.
In the aftermath of the fight, Smith's left arm looked very swollen and damaged.
Hearn explains that Smith suffered a detached bicep in the contest - but even without the injury his boxer would have still likely lost.
"You just saw the pound-for-pound king. Callum Smith is so tough. I think he detached his bicep in the second or third round but it didn't really matter. It was a masterclass from Canelo. I just left Smith's changing room and everyone is talking about Alvarez. He's just so good," Hearn told BBC Radio
"I'm proud of Callum. He never stopped throwing but he came up against the best fighter on the planet."