The National Football League suspended Dallas Cowboys defensive tackle Leon Lett for a minimum of one year Tuesday for violating the league’s substance abuse policy.

Losing Lett, one of the league’s premier players for the Cowboys’ top-ranked defense, could be a severe blow to the club’s chances of winning its fourth Super Bowl in five years.

Lett, who tested positive for cocaine, had appealed the one-year suspension on the basis that proper testing procedures were not followed.

NFL commissioner Paul Tagliabue denied the appeal.

“I’m fully satisfied that the program’s test collection and processing arrangements, to which the NFL and NFL Players Association have agreed, fully insures the integrity and accuracy of test results,” Tagliabue said in a statement. The statement said the NFL will have no further comment.

The NFL suspended Lett for four games last season for a first violation of the league’s substance-abuse policy. Lett had been required to undergo urine tests two to 10 times per month.

Lett, who signed a five-year, $12.8 million contract last year, will not be paid for the final three games of this season or the first 13 games of next season.

A source said Lett, represented by Washington D.C.-based attorney Craig Masback, had provided the league with a videotape showing the person responsible for collecting the urine samples had failed to follow proper procedures on some occasions.

Lett had adamantly denied testing positive for any illegal substance.

“This is a time for concern for Leon Lett the person,” said Cowboys owner Jerry Jones, who has vigorously denied knowing anything about a suspension. “Our thoughts are with him and his family, and we will continue to offer our help and support in any way we can.”