SAN DIEGO – San Diego Chargers linebacker Stephen Cooper was suspended by the NFL on Tuesday for four games for violating the league’s substance abuse policy.

The former University of Maine All-American will miss San Diego’s first four games of the 2008 season.

Cooper, 28, said in a statement he has accepted the suspension for his use of a stimulant that was recently added to the NFL’s List of Prohibited Substances and that the stimulant was not used prior to any game or with the intent to enhance performance.

“I regret that I mistakenly took a stimulant that I did not realize at the time was banned by the NFL,” Cooper said. “I support the NFL’s anti-doping policies and understand that I must serve a suspension even though the stimulant that I took was not used before any game and was not used to enhance my performance.”

The San Diego Union-Tribune reported Tuesday that Cooper had tested positive for ephedra, an ingredient commonly used in dietary supplements and cold medicines. Ephedrine, the active ingredient, is an amphetamine-like compound that can powerfully stimulate the nervous system and heart, according to the National Institutes of Health.

“I apologize to the NFL, my team, my coaches and to my fans, and I look forward to continuing to help the Chargers toward our goal of winning the Super Bowl in the upcoming season,” Cooper said.

Cooper’s suspension begins Aug. 30 following the Chargers’ final preseason game. He is eligible to return to the active roster Sept. 29 following the team’s Sunday game against the Oakland Raiders.

Cooper can participate in the team’s offseason program and in all preseason practices and games.

“Obviously, we’re disappointed, just as I know Stephen is,” said Chargers head coach Norv Turner. “Coop made a mistake and now must deal with the consequences. It’s unfortunate, but we’ll deal with it and move on.”

During 2007-08, Cooper’s fifth season in the NFL, he was San Diego’s leading tackler with 109, including 74 solo stops. The 6-foot-1, 235-pound linebacker had two sacks and two fumble recoveries.

In 2006, Cooper signed a five-year, $15 million contract.

The Massachusetts native had a stellar career for coach Jack Cosgrove at UMaine. He was named the A-10 Conference Defensive Player of the Year in 2001 (co-recipient) and 2002 and was twice selected as an AP All-American.

Cooper’s collegiate career ended on an inauspicious note after he pleaded guilty in December 2002 to possessing 1,262 anabolic steroid pills that he said he intended to take in the hope of improving his chances in the 2003 NFL draft.

Cooper, who denied having had the opportunity to use the drugs, was found with the pills in his duffel bag by the Maine State Police during a routine traffic stop of a friend’s vehicle.

In 2003, Cooper was sentenced at U.S. District Court in Bangor to one year of probation, 100 hours of community service and a $200 fine.

Cooper said he was subjected to NCAA drug testing five times during his UMaine career, but each time tested negative for illegal substances.