San Francisco ? Barry Bonds’ personal trainer refused to testify Thursday to the federal grand jury investigating the San Francisco slugger for perjury.

Greg Anderson, who served three months in prison after pleading guilty last year for his role in the Bay Area Laboratory Co-Operative steroid scandal, could be sent back to prison if found in contempt of court for refusing to testify.

A hearing will be held next Wednesday, and Judge William Alsup said he would rule next week on whether Anderson should be found in contempt.

Anderson’s attorney, Mark Geragos, said his client should not have to testify because he was the victim of an illegal government wiretap that he said resulted in a recording of Anderson saying he provided Bonds with “undetectable” drugs to help him beat baseball’s drug testing program in 2003.

The details of the recording were first reported in October 2004 by the San Francisco Chronicle, which obtained a copy from a confidential news source.

Prosecutor Jeff Nedrow revealed Thursday that his office had obtained a copy of the recording last summer.

Alsup ruled that the recording was “not a wiretap, but a privately recorded conversation with a witness,” and that there was no legal reason for Anderson not to testify.

Nedrow said he wanted to question Anderson about the recording and a “mountain” of other evidence.