Saul 'Canelo' Alvarez recognised the damage to Callum Smith's left arm as early as the fourth round after dominating the Briton, who Eddie Hearn says may have a detached bicep or triceps.
Alvarez (54-1-2) inflicted a first career defeat on Smith (27-1) in Texas on Saturday to clinch the WBA and WBC super-middleweight titles by unanimous decision.
Following the fight, which the judges scored 119-109, 119-109, 117-111 in favour of Alvarez, Smith refused to make any excuses for the one-sided loss but pictures showed gruesome damage to his arm.
Asked about the injury to his opponent, Alvarez replied: "It was the fourth or fifth round that I obviously saw it was hurting, I have much faith in those type of punches.
"It was the 12th round I saw it was really hurt, we know he has a really good left punch that's what we worked on at the gym."
Matchroom promoter Hearn offered an update on Smith, who will undergo further examination to ascertain the extent of the injury.
"I saw it I think in the 11th round, Canelo looked at it and pointed at it, it was getting bigger and bigger," Hearn said.
"It's not diagnosed yet, some people in the dressing room think he broke his arm, it makes sense he took a lot on it.
"I think it looks like a detached bicep or triceps. He has a lump on the outside of his arm, the doctor said it's a torn bicep or triceps so he's going to need a scan.
"I think it happened as early as the second or third round, but he didn't for one second say 'I couldn't do this or I couldn't do that' it just got progressively worse.
"He's a very humble guy he just held his hands up and said Canelo was the better man."
Shortly after the bout, WBO super-middleweight champion Billy Joe Saunders tweeted to call out Alvarez, a fight Hearn says that, in theory, is easy to put on.
"[I could make that fight] tonight," he added.
"I mean the big problem is when you talk about the revenue for any show is that gate. Tonight we were blessed with 12,000 people, it felt like my first ever show I went to as a kid.
"We already had a deal for Billy Joe Saunders to fight Canelo Alvarez in May, he's tweeted tonight that he wants a shot.
"Canelo walked past me after and said that's three who's next? We tried with Rocky Fielding, Daniel Jacobs - we've got two more in Billy Joe Saunders and Gennady Golovkin [who Alvarez has faced twice, drawing the first fight and winning the second].
"He loves the belts, he wants to face the champions."