(AP) — Lamont Peterson’s scheduled May 19 rematch with Amir Khan in Las Vegas has been called into doubt after a Nevada boxing official said Peterson failed a doping test.

Peterson, 28, the WBA and IBF junior welterweight champion, tested unacceptably high for synthetic testosterone in a urine test administered in March by the Las Vegas-based Voluntary Anti-Doping Association, Nevada Athletic Commission executive Keith Kizer said Tuesday.

Separate tests on a second sample from the same time were reported positive last Thursday, according to a report Kizer said he received Monday from Dr. Margaret Goodman, VADA chief executive and a former ringside physician.

“Unless there’s some real obvious and legitimate reason for the positive test, he’s not fighting,” Kizer told The Associated Press.

Kizer said Peterson (30-1-1, with 15 KOs) isn’t currently licensed to fight in Nevada, but would usually get routine approval in the next several days for the fight scheduled next week at the Mandalay Bay resort.

Now, Peterson needs to win an appeal to the five-member commission, which isn’t scheduled to meet until May 21.

Kizer said Peterson’s Washington, D.C.-based lawyer, Jeff Fried, promised him an explanation by the end of the day Tuesday.

Khan’s promoter, Richard Schaefer of Golden Boy Promotions in Los Angeles, called it premature to say whether the Peterson-Khan fight will be held.

But if Peterson can’t fight, Khan won’t face a substitute opponent, Schaefer said.

“If he is allowed to fight, obviously we will fight,” Schaefer said. “We’re going to wait to see what the Athletic Commission decides. It would be impossible to find an opponent within a week and a half for a fight of this caliber.”

Goodman and Dr. Edwin “Flip” Homansky, a former Nevada Athletic Commission member also affiliated with the Voluntary Anti-Doping Association, declined to comment on Peterson’s test results. They cast VADA as a neutral testing agency.

Peterson and Fried were notified April 13, but didn’t share word of the first positive steroid test by the UCLA Olympic Analytical Laboratory in Los Angeles.

“It appears as though Mr. Peterson and Mr. Fried … chose not to notify third parties at that time in the hope that Mr. Peterson’s “B” sample would test negative,” Goodman said.

The document said the second test was conducted at the UCLA Olympic lab April 30 with at least one Peterson representative present.

Kizer said Fried told him Peterson recalls receiving testosterone treatment from a doctor before his first fight against Khan ended in controversy last December in Washington.

“He’s saying Peterson’s only real fault was that he failed to report therapeutic use of testosterone,” Kizer said.

Khan (26-2, with 18 knockouts) lost his WBA and IBF belts in a split-decision loss to Peterson on Dec. 10, but was granted a rematch after complaining about the referee’s decision to deduct him two points for pushing. He also was upset by the presence of an unauthorized man at ringside who was seen distracting an official.