National Basketball Association is involved into match-fixing by referee as FBI gambling investigation plunged into retired referee Tim Donaghy on Monday amid disturbing reports.

The New York Post, citing an unnamed source, reported Donaghy was ready to cooperate with authorities and name other referees, players, coaches and gambling figures who might be involved in the league-rocking scandal.

A terrified Donaghy, whose name was first unearthed during wiretaps in the Gambino mobster case, had received death threats and received police protection in the wake of the probe, the Post reported, saying relatives urged him to join a witness relocation program.

Federal investigators are looking into claims Donaghy, 40, worked with mobsters to fix margins and outcomes of NBA games to pay off gambling debts.

He resigned earlier this month after a 13-year career following allegations that he bet on games that he officiated.

No specific games in which he was involved have been revealed as being under scrutiny, although among those he handled was a game in the San Antonio-Phoenix playoff series.

San Antonio beat the Suns and swept to the NBA crown over Cleveland in the finals.

NBA commissioner David Stern has called a Tuesday morning news conference where he will answer questions on the matter. He made a statement Friday when news of the scandal became public.

The New York Daily News, citing an unnamed source, reported NBA officials had a private investigator following Donaghy more than a year ago but continued to assign him to games into the second round of the NBA playoffs last May.

The News also reported that Donaghy received an above-average evaluation from superiors last season, when Donaghy called the most technical fouls of any referee in the NBA.