The National Football League has indefinitely suspended star quarterback Michael Vick of the Atlanta Falcons after he admitted in court papers to involvement in an illegal dogfighting ring.

NFL Commissioner Roger Goodell said in a letter Friday that Vick's conduct was "not only illegal, but also cruel and reprehensible." He said Vick's actions have hurt his team, the NFL and NFL fans.

The league said Vick's suspension is without pay.

Vick filed his plea agreement Friday in federal court, admitting to conspiracy in a dogfighting ring and helping to kill pit bulls. But he denied ever betting on the fights, only bankrolling them.

Vick is scheduled to formally enter his plea on Monday in U.S. District Court in Richmond, Virginia. That is the state where it was discovered the dogs were trained, sheltered and some allegedly even tortured before they were killed on property Vick owned.

Three co-defendants previously pleaded guilty. For Vick's plea agreement, the government is expected to recommend a sentence of 12 to 18 months in prison. However, the conspiracy charge is punishable by up to five years in prison, and the judge is not bound by any recommendation or by the sentencing guidelines. Vick also faces up to $250,000 in fines.

It is expected to be several months before the star quarterback is sentenced.

Vick had been one of the NFL's most popular players. He has been barred from the Falcons training camp, but neither the NFL nor the team has taken further action.

It is uncertain how a possible prison term would affect Vick's NFL career.

Some information for this report provided by AP.