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.