Source: Clemens Used Steroids While with the Yankees

— -- A former New York Yankees strength trainer says information he provided to the George Mitchell investigation regarding supplying Roger Clemens and Andy Pettitte with steroids is included in the Mitchell report scheduled to be released later today, a source close to the trainer told ESPN The Magazine's Shaun Assael.

Brian McNamee, who worked for the Yankees and as a personal trainer for Clemens and Pettitte, also told investigators that on at least one occasion, Clemens was in possession of steroids from another supplier, the source said.

The source said McNamee told investigators he supplied Clemens with steroids while Clemens was with the Yankees, and prior to Clemens joining the team.

Randy Hendricks, Clemens' agent, did not immediately return a message seeking comment, according to The Associated Press.

Also, The Bergen (N.J.) Record, citing a baseball industry official, says "several" prominent Yankees will be named in the Mitchell report. The paper said the source spoke to a third party who had seen the final report.

"It's going to be a rough day in the Bronx," the paper quoted the source as saying.

Mitchell plans to release his report at 2 p.m. ET Thursday at a news conference in New York City.

Baseball commissioner Bud Selig will hold his own news conference 2½ hours later.

The Major League Baseball Players Association sent an e-mail to agents Thursday morning, a copy of which was obtained by ESPN.com's Amy K. Nelson. In it, it said: "We cannot confirm any of the press stories predicting what the report will say. We have not been given an advance copy of the report and we have not been informed of its contents. We requested from Senator Mitchell and the Commissioner's Office a copy of the report in advance, so that we'd have a meaningful opportunity to review it. They denied our request. We will be given the report at 1:00 PM, an hour before its public release, but only based on our pledge not to disclose its contents before 2:00 PM. The report is expected to exceed 400 pages, including appendices.

"Some have asked for our advice about public comment. As always, you are free to do as you wish, but we suggest that, for today at least, you decline general comment on the report and respond only on behalf of a particular player named in the report."

Selig told the Chicago Tribune that he hadn't seen the report, but he was proud it is coming out.

"People can say Bud was just trying to cover his butt or take care of his legacy or whatever," Selig said, according to the Tribune. "I say [bleep] it. This needed to be done, and now we've done it. I'm just happy it will be out there and we can move on. I'm proud of it."

Scott Boras, who represents a number of high-profile players including Yankee third baseman Alex Rodriguez, told The Los Angeles Times he hadn't read the report. He did, however, say he's wary because he believes "the concerns of due process and the standards that apply to it are relatively unknown. Certainly, any results that occur from the report have to be looked at in the light that this is not a collectively bargained effort."

"I'm going to assume that a lot of the basis for this is hearsay information," Boras said, according to The Times. "It's not based on any kind of clinical testing, so it is widely a product of hearsay testimony. Without clinical testing or hard evidence, any report like this has to be reviewed with great scrutiny."