The quarterback's absence from the New York Jets at the end of the season indicates a setback in his drug rehabilitation and previously undisclosed diagnosis of bipolar disorder, sources told ESPN's Chris Mortensen.
He has entered a treatment center to deal with both afflictions, the sources said. Carter previously entered treatment programs in January of 2003 in the Boston area and again in the summer of 2004 at the John Lucas Treatment Center in Houston, Mortensen reported.
The Dallas Cowboys released Carter on Aug. 4 amid reports he failed a drug test. Carter was already in the NFL substance abuse program for his first positive test.
A third positive test would bring a four-game suspension.
The NFL Players Association has filed for arbitration in the case, saying the Cowboys violated the collective bargaining agreement. A date for the non-injury grievance could be set this week.
Three weeks after his release by the Cowboys, Carter signed with the Jets. The week before their playoff game with the Steelers, the Jets announced that Carter had left the team to return to Georgia to be with his ailing mother.
Carter signed a one-year contract for $455,000 in base salary with the Jets. Carter's contract with the Cowboys included $455,000 in base salary in 2004 and a $260,000 roster bonus.
Information from The Associated Press was used in this report.