Houston Texans linebacker Brian Cushing tested positive for HCG, a fertility drug that's on the NFL's banned substance list, a person familiar with the case told The Associated Press on Tuesday.
The linebacker had one positive test last September, then subsequently tested negative several times, said the person, who spoke on condition of anonymity because the results were supposed to remain confidential.
"He had one low-level positive test for HCG in September, and then every test after that was negative," the person said. "He has said he has no idea where the positive test came from."
The NFL has suspended Cushing for the first four games of the 2010 season. He won the NFL Defensive Rookie of the Year honor in January for outstanding on-field performance, but the AP is taking a revote for the award, plus for All-Pro outside linebacker. Votes are due by noon ET Wednesday, and Cushing remains a candidate.
Cushing, a first-round draft pick out of USC, was a runaway winner for the rookie award in balloting by a nationwide panel of 50 sports writers and broadcasters who cover the league. He received 39 votes, easily beating Buffalo Bills safety Jairus Byrd, who had six.
ESPN first reported Tuesday that the banned substance was human chorionic gonadotropin, which is widely taken by steroid users to help restart natural testosterone production. HCG can mitigate the side effects of ending a cycle of drugs. It's also used to induce ovulation and treat ovarian disorders in women.
Last year, Major League Baseball gave Los Angeles Dodgers outfielder Manny Ramirez a 50-game suspension for testing positive for HCG.
The person familiar with Cushing's case said medical experts have talked about a surge in HCG levels for a man after a workout or after ejaculation. However, U.S. Anti-Doping Agency spokeswoman Erin Hannan denied that.
"You would not see a natural spike of HCG after a workout or ejaculation," Hannan told The Associated Press. "You would only detect it in urine by actually having taken it."
Texans owner Robert McNair on Monday criticized the lack of information provided teams when a player has failed a drug test. He said he would like the testing system and lack of communication with the teams addressed in the next collective bargaining agreement.
NFL Players Association executive director DeMaurice Smith responded to those comments Tuesday in a statement released by the union.
"Sport is at its best when fans can witness great achievements under the rules of fair play," Smith wrote. "Players who break those rules cheat the game, cheat the fans and cheat themselves. The players want a clean game as well as a clean process for enforcing those rules. We intend to address both in the collective bargaining process to make the system better."
Cushing is suspended without pay until Oct. 4, although he can participate in offseason workouts, training camp and preseason games. He will not be eligible for next season's Pro Bowl -- he made the AFC team last January but didn't play, citing several injuries -- or any NFL-sponsored awards.
Needing depth at linebacker because of Cushing's suspension, the Texans are bringing back Danny Clark, who played for the New York Giants the last two seasons after leaving Houston. Clark told KRIV-TV on Tuesday that he had agreed to a one-year contract with the team.
Clark, a 10-year NFL veteran, spent the 2007 season with the Texans and appeared in each game, finishing with 51 tackles. His best seasons came with the Oakland Raiders in 2004 and 2005, when he had 129 and 113 tackles, respectively.
Clark also has played for the Jacksonville Jaguars (2000-03) and New Orleans Saints (2006).
The Associated Press contributed to this report.