Manny Pacquiao could be out of action for a year as he prepares to have surgery on his injured shoulder.
The 36-year-old blamed the injury for Saturday’s points defeat by Floyd Mayweather, claiming it stopped him using his right hand during the bout.
Pacquiao’s adviser, Michael Koncz, denied claims the Filipino’s camp deliberately did not declare the injury to the Nevada Athletic Commission.
Surgeon Neal ElAttrache told ESPN that Pacquiao had a “significant tear”.
He added the injury was likely to sideline the fighter for between nine and 12 months.
Top Rank promoter Bob Arum claimed Pacquiao injured his shoulder about two and a half weeks before Saturday’s fight in Las Vegas.
Pacquiao said he wanted a pre-fight injection in the shoulder but the Nevada Athletic Commission refused.
Commission chairman Francisco Aguilar said he first knew about the injury two hours before the fight, when Pacquiao’s camp requested an anti-inflammatory shot be administered.
Officials denied the request and Aguilar blamed Pacquiao for not disclosing his injury sooner.
Mayweather, 38, scored a unanimous points victory in the four-belt unification bout at the MGM Grand Garden Arena.
The win extended the American’s unbeaten record as a professional to 48 fights.
Pacquiao’s surgery means any rematch is unlikely, with Mayweather insisting he will retire in September after one more fight.
Britain’s Amir Khan says Mayweather’s manager told him “let’s get that fight on” after Saturday’s bout.