Two US men accused with Atlanta Falcons quarterback Michael Vick of organising dog fights have pleaded guilty.
Michael Vick has pleaded not guilty to dog-fighting charges
Vick, 27, pleaded not guilty at an earlier court hearing and is due to stand trial on the charges in November.
According to US media reports, Vick's lawyers have been discussing a possible plea deal. He may face additional federal charges of racketeering.
Vick has been barred from pre-season training. He faces a $250,000 fine and up to five years in jail if convicted.
Any guilty plea or conviction is also likely to result in a lengthy ban from the NFL, under its personal conduct policy for players.
About 30 animal rights activists gathered outside the courtroom in Richmond, Virginia, for Friday's hearing, the Associated Press news agency reports.
Purnell Peace, 35, of Virginia Beach, and Quanis Phillips, of Atlanta, both pleaded guilty to charges of conspiring to sponsor a dog-fighting venture. They will be sentenced later this year.
A fourth defendant in the case had already changed his plea to guilty and agreed to co-operate with the prosecution case against Vick.
Vick issued a statement in July saying that he looked forward to clearing his name.
Police who searched his property in April allegedly found pit bull dogs and dog-fighting paraphernalia.
According to court papers, dogs that lost fights were sometimes killed by electrocution or hanging.
Since the charges were brought, pressure has been mounting on the league and the Falcons, particularly from animal-rights groups.
Activists also want companies that have endorsements deals with Vick to cut their ties.
Vick, the first overall pick in the 2001 college draft, last season became the first quarterback ever to rush for more than 1,000 yards.
Atlanta played their first pre-season match against the New York Jets on 10 August, with the regular season beginning in Minnesota on 9 September.