HELENA, Mont. — Former NFL and Washington State quarterback Ryan Leaf has been moved from a drug-treatment center to the Montana State Prison for threatening a staff member and violating his treatment plan, a corrections official said Thursday.

The former San Diego Chargers quarterback was charged last spring with breaking into two houses and stealing prescription painkillers near his hometown of Great Falls. He pleaded guilty in May to burglary and criminal possession of dangerous drugs, and his five-year sentence called for spending nine months in a locked drug-treatment facility as an alternative to prison.

Leaf said then he was looking forward to the treatment at Nexus Treatment Center in Lewistown. But on Thursday, the Montana Department of Corrections released a statement by Great Falls regional probation and parole administrator Dawn Handa that said Leaf, 36, will now serve his sentence in the Deer Lodge prison.

"The Montana Department of Corrections terminated Leaf from the treatment program and placed him in prison after he was found guilty of behavior that violated conditions of his drug treatment program. The violations included threatening a program staff member," Handa wrote.

Leaf's attorney, Kenneth Olson, did not return calls.

Pam Bunke, adult community corrections division director, wrote that Leaf was too great a security risk to leave in a community setting, and that staff had exhausted all resources in keeping him there.

Leaf told his roommate at the treatment center that he wanted to drag a program staffer by his hair, according to the Department of Corrections document approving Leaf's transfer to prison.

Leaf also wrote in three "thinking error reports" that he wanted to throw the staffer against the wall and smash his glass into the man's head.

Thinking error reports are part of the treatment program meant to help participants monitor their potential problems and help them recognize and cope with the source of their addiction.

Leaf was moved out of the Lewistown center Dec. 29. He was held in the Fergus County Jail until he was transported to the Deer Lodge prison Wednesday, said corrections spokesman Bob Anez.

Leaf will remain in the state prison until at least June 30, when he becomes eligible for parole, Anez said. That does not mean he will be released, but he will receive a hearing.