Former NFL quarterback Ryan Leaf is considered to be the biggest NFL draft bust of all time and he isn't losing that moniker anytime soon.

According to ESPN.com, 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.

Leaf was quarterback for the San Diego Chargers in the NFL and played for the Washington State Cougars before getting drafted as the No. 2-overall pick behind Peyton Manning. He was in the treatment program after being charged last spring with breaking into two houses and stealing prescription painkillers near his hometown of Great Falls.

Leaf pleaded guilty in May to burglary charges and criminal possession of dangerous drugs, and he was in the locked drug treatment facility as an alternative to prison, which called for a five-year sentence.

At the time it appeared Leaf had received a fortunate break and

Leaf said then that 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 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 said in the statement.

According to ESPN.com, Leaf attorney Kenneth Olson did not return any calls for comment.

Adult Community Corrections Division director Pam Bunke wrote that Leaf was a security risk and that he did not follow protocols and was threatening towards the staff. The report says Leaf told his roommate in the treatment program 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 mentioned threatening comments in reports he was required to write, including saying he "wanted to throw the staffer against the wall and smash his glass into the man's head."

This has been a repeated issue for Leaf, who also got in trouble at a disciplinary hearing held Jan. 9 in which a hearings officer found Leaf guilty of threatening another person or his possessions, according to a summary by the Department of Corrections. Furthermore, Leaf was found guilty of wearing clothes he was told not to wear and volunteering his services when directed not to, according to the summary.

The report said that Leaf was "less than cooperative" and that multiple attempts had been made to get him into compliance with the rules.

"He got angry, swore at staff, refused to sign off on the witness form and threw the hearing notification papers on the floor," the report said.

Leaf has been troubled for many years since washing out of the NFL. He faced drug charges in 2010 in Texas and then had the incident in Montana. According to the AP, an investigation began in March 2011, after Great Falls postal workers reported they were suspicious of frequent packages Leaf received by paying COD charges of $500.

Leaf was eventually found with a container with 28 oxycodone pills inside and another container with a prescription made out to an acquaintance. The Great Falls Tribune first reported Leaf's imprisonment Thursday.

As the No. 2 pick in the draft, Leaf was highly regarded, but never could adapt to the NFL. The Chargers were set back a number of years after his failure and he finished his career with just 3,666 yards passing with 14 touchdowns and 36 interceptions. The choice between Leaf and Manning is now looked at as legendary as the Colts opted to pick the Tennessee quarterback.

Leaf is considered to be the biggest bust in NFL history, while Manning is considered one of the best quarterbacks ever. Manning has won a Super Bowl and four MVP awards, while the Chargers went just 5-11 in Leaf's first season.

According to the LA Times, Leaf also faces the revocation of a 10-year probationary sentence for a 2010 drug and burglary conviction in Texas.