Manny Pacquiao's camp accused the Nevada Athletic Commission on Monday of denying them treatment for an injury to his right shoulder which will now require surgery to repair.

Pacquiao, who lost a unanimous decision to Floyd Mayweather in their welterweight unification fight on Saturday, is expected to undergo surgery later this week for a torn rotator cuff, ESPN reported Monday.

Dr Neal ElAttrache described the tear as "significant" and said Pacquiao could be out between nine and 12 months.

ElAttrache is one of the most-respected surgeons in North America, having operated on New England Patriots quarterback Tom Brady, Los Angeles Dodgers pitcher Zack Greinke and Los Angeles ­Lakers star Kobe Bryant.

Pacquiao and Mayweather met at the MGM Grand in Las Vegas in one of the most-­anticipated showdowns in boxing history which promises to be the richest fight ever with revenues of about $400 million.

The super fight also ­cemented Mayweather as the top pound-for-pound fighter of the era but that was before ­severity of Pacquiao's injury was revealed.

The southpaw clearly had difficulty with his right hand during the 12-round title fight as he landed just 18 jabs, compared to 67 for Mayweather. The injury also limited Pacquiao's power punches as he connected on just 27 percent compared to the defensively minded Mayweather who connected on 48 percent.

Pacquiao's camp said the Commission refused them treatment on fight night ­despite them having prior approval to use an anti-inflammatory ­injection by the United States Anti-Doping Agency, which conducted random drug testing on the boxers in the buildup to the fight.

Pacquiao's camp had planned to give him Toradol, a non-steroid anti-inflammatory, just before the fight, but the Commission stepped in and halted the treatment.

Pacquiao said he hurt the shoulder in training camp some three weeks before the bout, and they considered postponing the contest dubbed the "Fight of the Century." His camp said when the injury first happened, Pacquiao visited the ElAttrache's Kerlan Jobe Orthopedic Clinic in Los Angeles and he was told to treat it with rest before resuming his heavy training regime for the fight. After some rest, Pacquiao continued to work with trainer Freddie Roach who felt, along with promoter Bob Arum, that the injury had improved enough to allow the fight to go ahead.