Floyd Mayweather Jr. has been ordered to begin giving testimony Friday in a defamation case against him filed by rival fighter Manny Pacquiao.
Mayweather is being sued over statements accusing Pacquiao of taking performance-enhancing drugs.
The two, considered the best pound-for-pound fighters in the world, have repeatedly failed to reach terms on what could be the richest bout in boxing history.
Federal magistrate Judge Robert Johnston denied an emergency motion Thursday that would have allowed Mayweather to delay testifying.
Mayweather claimed that he needed to concentrate on his upcoming fight against Victor Ortiz, which is scheduled for Sept. 17.
Mayweather also faces felony charges stemming from a domestic argument and misdemeanour harassment and battery charges in separate cases.