A DRUGS test on Oliver McCall taken after his WBC heavyweight title fight with Lennox Lewis has proved negative.

Nevada boxing regulators took a urine sample from McCall after he lost in the fifth round on Friday night, when he refused to continue fighting and broke down in tears.

"He gave us a urine test with no complaints right after the fight despite his agitated state," Nevada Athletic Commission director, Marc Ratner, said. "It's important to know it was negative."

McCall's $3 million purse from the fight continues to be held pending an investigation into why he stopped both throwing punches and defending himself.

Ratner said the commission has little other authority than to fine McCall or suspend his boxing licence. But he predicted others could go to court to settle grievances over the bout.

"This will not just go away," Ratner said. "It will likely end ups in some civil court."

McCall entered outpatient drug rehabilitation after being arrested for throwing a Christmas tree during a drunken rampage.