David Stern insisted allegations a former referee bet on games was an isolated case and called it the worst situation he had experienced during his tenure as commissioner.

"Mr. Donaghy is the only referee alleged to have bet on NBA games and disclosed confidential information to others," Stern said Tuesday during a packed news conference. "I'll say it again, I understand this is an isolated case."

The FBI is investigating former referee Tim Donaghy for allegedly betting on games he officiated during the last two seasons. He is expected to turn himself in at U.S. District Court in Brooklyn later this week or early next week, according to a person familiar with the investigation.

"We understand he's accused of betting on games in the NBA," Stern said. "We're not positive it's games he worked."