The fallout from the "Fight of the Century" became murkier on Monday with possible lawsuits in the works and Manny Pacquiao likely to face disciplinary action for failing to disclose a pre-bout shoulder injury.

Filipino Pacquiao lost on a unanimous decision to undefeated American Floyd Mayweather Jr in a heavily hyped welterweight showdown in Las Vegas on Saturday that is expected to be the top grossing prize fight of all time.

Barely one hour after the contest ended, Pacquiao's promoter, Bob Arum, said the 36-year-old southpaw had been hampered by an 'old' injury to his right shoulder.

On Monday, an MRI scan in Los Angeles confirmed the boxer has a torn rotator cuff that will require surgery.

The major problem here is that apparently neither Pacquiao nor his team informed the Nevada Athletic Commission about the shoulder issue until a couple of hours before the start of the fight when they asked for an anti-inflammatory injection.

At that point, it was too late for the commission to investigate whether or not Pacquiao was suffering a genuine injury and there were no MRIs or medical paperwork to support the claim made by the boxer's team, the commission said.

While the commission was seemingly kept in the dark, and clearly no boxer wants to give an opponent any hint of possible weakness or injury ahead of a fight, the United States Anti-Doping Agency (USADA) was fully aware of Pacquiao's injury.

The Filipino suffered the injury during a sparring session at the Wild Card Boxing Club in Los Angeles last month and USADA, after being consulted by Team Pacquiao, permitted treatment through Toradol, a non-steroidal anti-inflammatory.

The commission was in overall control, yet when Team Pacquiao filled in its pre-fight medical questionnaire on Friday, a query about any shoulder injury was marked clearly "No" before the form was signed by Pacquiao and his advisor.

The fact that Pacquiao did not disclose his injury until the night of the fight could also lead to possible lawsuits from boxing fans who feel cheated after paying record sums for either tickets in the MGM Grand Garden Arena or pay-for-view (PPV).

Some of the coveted ringside spots in the 16,800-seat Garden Arena demanded up to $350,000 on resale site StubHub while a record $300 million or more is expected in PPV revenue from at least three million customers who paid $100 to watch.

Pacquiao, who is renowned for his attacking style, connected with just 81-of-429 punches on the night while the defence-minded Mayweather landed 148-of-435.

Source: Al Jazeera and agencies