Barry Bonds's weight trainer said on a secretly recorded tape that the San Francisco Giants star took an undetectable performance-enhancing drug during the 2003 season, the San Francisco Chronicle reported Saturday.

Greg Anderson, a longtime friend of the Giants outfielder, also said he expected to be tipped off before Bonds would have to take a drug test.

Anderson is a central figure in a professional sports steroids case that has focused on the San Francisco-area BALCO nutritional laboratory. The accused have pleaded not guilty.

"The whole thing is, everything that I've been doing at this point, it's all undetectable," Anderson said on the tape, the newspaper reported.

Of baseball's drug test, Anderson reportedly said: "It's going to be in either the end of May or beginning of June. So after the all-star break . . . we're like [expletive] clear."

The paper said the nine-minute recording, which was apparently made early in the baseball season, was provided by a source familiar with Anderson who asked not to be identified.

Commissioner Bud Selig, in Boston for the American League Championship Series, said he had not read the Chronicle story but he didn't feel it would further tarnish the sport's reputation.

"It's a further manifestation why we need a strict steroid policy," Selig said. "But until there is proof there's something wrong . . . all you have is a series of allegations."

Anderson declined to comment on the report.

His lawyer, Anna Ling, said the voice on the recording did not sound like Anderson's, and that a 90-second portion of the tape she reviewed was full of gaps and background noise.

Bonds's attorney, Michael Rains, did not immediately return a message left at his office. Rains told the Chronicle that the tape was "simply another below-the-belt bash of Barry Bonds."

Anderson has denied giving performance-enhancing drugs to Bonds.