Floyd Mayweather says "winners win and losers have excuses" after Manny Pacquiao blamed a shoulder injury for his loss to the American in Las Vegas.
Pacquiao is being sued in Nevada after being accused of lying about the shoulder injury he suffered pre-fight.
The Nevada Athletic Commission (NAC) says Pacquiao, 36, did not declare the problem, but the Filipino claims a treatment plan was agreed with United States Anti-Doping Agency (Usada).
He could face a fine or suspension.
Pacquiao is being sued by two people in Nevada who have alleged the boxer defrauded ticket buyers, television viewers and gamblers.
They have opened lawsuits just hours after the NAC accused the fighter of being dishonest by not declaring his injury on a pre-fight questionnaire - which has also led to suggestions he could face a charge of perjury.
The state attorney general's office is investigating.
However, Pacquiao's adviser Michael Koncz said he took "full responsibility" for the "inadvertent mistake".
"Number one, Manny didn't check the box," Koncz said. "I checked it. We weren't trying to hide anything. I just don't think I read the questionnaire correctly."
Pacquiao blamed his injury for his points defeat to undefeated Mayweather, 38, claiming it stopped him using his right hand.
His camp claimed Usada had been notified of his treatment and plans for an anti-inflammatory shot on fight night.
But Usada was only charged with monitoring anti-doping issues and NAC officials prevented the injection, saying they had not been told about Pacquaio's shoulder issue.
No date has been set for surgery to repair the "significant tear" and although Pacquiao will face up to a year out, ESPN claims Mayweather is open to a re-match in 12 months time.
Mayweather scored a unanimous points victory in the four-belt unification bout at the MGM Grand Garden Arena, the win extending the American's unbeaten record as a professional to 48 fights.
He has said he intends to retire after one more fight, possibly in September, with Britain's Amir Khan among the potential opponents.