IRVING, Texas -- Dallas Cowboys fullback Robert Thomas, who is out for the season after tearing ligaments in his left ankle, has reportedly violated the NFL's substance-abuse policy.

Several sources told The Dallas Morning News on Wednesday about the violation.

Cowboys spokesman Rich Dalrymple would not comment on the report.

"The organization does not comment" about allegations of substance abuse, he told The Associated Press on Thursday.

Cowboys owner Jerry Jones and vice president Stephen Jones also declined to comment.

Steve Weinberg, Thomas' agent, referred all calls to Thomas without comment. A phone number for Thomas, injured late in the Cowboys' 9-7 victory over Washington on Oct. 15, was not listed and he could not reached Thursday by the AP for comment.

One source told the Morning News that Thomas has not been fined any game checks by the league because he is appealing the violation.

Thomas, the only fullback on the roster before he was injured, was placed on injured reserve on Monday. He underwent surgery on Friday to repair damage in his ankle.

The Cowboys signed Thomas to a three-year contract that guarantees him $1 million in the first two years because he was about to sign an offer sheet from the Chicago Bears.

The contract pays Thomas $418,000 this season, $750,000 in 2002 and $1.18 million in 2003. He also received a $300,000 signing bonus.

A free agent linebacker in 1998, Thomas moved to fullback in 1999 and became a starter midway through the season following a career-ending neck injury by fullback Darryl Johnston.

The 6-foot-1, 270-pound Thomas was more of a pure blocking back, with just 11 touches -- six carries for 40 yards and five catches for 19 yards -- before his injury. He was a lead blocker for Emmitt Smith.

"I am blessed because I've come a long way in a couple of years, but I feel like I put in the hard work to succeed," Thomas said the day before he signed his new contract last March.