Sources told ESPN and ESPN.com that Carter recently failed a drug test. Carter already was in the NFL substance-abuse program, having tested positive for an illegal substance in the past, according to ESPN's Chris Mortensen. ESPN.com has learned that Carter spent time at a drug rehabilitation facility within the past 18 months.
League sources told ESPN.com that despite the positive test Carter is not under suspension.
A source close to Carter vehemently denied a broadcast report that the quarterback had tested positive for cocaine.
Carter, the starting quarterback for the last three seasons, left the Cowboys' training camp in Oxnard, Calf., early Wednesday. The release of Carter is expected to be official later Wednesday afternoon and addressed by coach Bill Parcells at his daily press briefing between practices. Owner Jerry Jones has confirmed the move.
A three-year veteran, Carter had started 31 games in his career, including all 16 in 2003, when he led Dallas to a 10-6 record and a wild card spot, the first postseason appearance by the team since 1999. The former University of Georgia standout was a second-round pick in the 2001 draft.
"I think I probably speak for all the guys of how disappointed
we are that Quincy is no longer going to be part of this team,"
Testaverde said. "But at the same time we know we have to look
forward to getting things down and go out and win games."
After practice, Parcells gave the players some sort of
explanation about Carter's departure, but players declined to
comment on the discussion.
Carter's career has been a roller coaster, with flashes of brilliance often followed by very uneven performances. Just days ago, when asked about his starter for this season, Parcells acknowledged that Carter had "a leg up" on the No. 1 job.
What changed that, at least for now, is unknown.
In his three NFL seasons, Carter completed 507 of 902 passes for 5,839 yards, with 29 touchdown passes, 36 interceptions and a passer rating of 70.0. He threw for 3,302 yards last season, his best year in the league.
Testaverde, 40, was signed by the Cowboys in the spring after the New York Jets released him for salary cap reasons. Testaverde played for Parcells in New York and, even before the Jets freed him, it was obvious he was headed to Dallas for a reunion with the coach.
The 17-year veteran has completed 3,334 of 5,925 passes for 40,943 yards, and he has 251 touchdown passes and 235 interceptions.
The other two quarterbacks on the roster are rookie Drew Henson, the former Michigan star who in February abandoned his pursuit of a baseball career with the New York Yankees to return to football, and second-year pro Tony Romo.
Len Pasquarelli is a senior writer for ESPN.com. Information from The Associated Press was used in this report.