Oakland senior assistant Bruce Allen said he knew of no suspensions. He criticized the report but wouldn't confirm or deny the accusation of positive tests.
"The league's program on testing and information on testing are extremely confidential," Allen said Sunday before the Raiders' game against the Minnesota Vikings. "So any reports out of that, someone's either violating the law or making them up. I hope they're able to find the people who spread false rumors."
CBS' "The NFL Today" and SportsLine.com reported that defensive tackle Dana Stubblefield, center Barret Robbins, former Denver Broncos linebacker Bill Romanowski and defensive tackle Chris Cooper were notified in letters from the NFL this past week that they tested positive for THG, or tetrahydrogestrinone. It wasn't clear when the tests were conducted or the urine samples were taken.
"That's a situation that's out there," Robbins said after the Raiders' 28-18 win over Minnesota. "I haven't been notified about it. I don't think it's right the way it's being handled. That's about all I've got to say about that."
Agents for the players didn't immediately return calls from The Associated Press on Sunday. NFL spokesman Greg Aiello wouldn't comment.
"The process has been violated by the information coming out," said Raiders defensive end Trace Armstrong, the players' association president.
Stubblefield and Cooper, along with running back Tyrone Wheatley and fullback Chris Hetherington, appeared Thursday before a grand jury probing a nutritional supplements lab — the Bay Area Laboratory Co-Operative.
An attorney for lab founder Victor Conte has confirmed his client is the target of the grand jury probe. Conte has been accused by the U.S. Anti-Doping Agency of supplying athletes with THG. He has denied the report.
Romanowski throughout his career has used nutritional supplements.
In 2001, Douglas County, Colo., prosecutors dropped charges against Romanowski's wife, Julie, who had faced eight counts of illegally obtaining the diet drug phentermine for her husband.
Romanowski had been acquitted on related charges the month before.
Prosecutors claimed Romanowski took phentermine to enhance his play; the defense said he took it to suppress his hunger before games. The drug is not banned by the NFL.