In his upcoming autobiography, Agassi admits he used crystal meth in 1997 and failed a drug test — a result he says was thrown out after he lied by saying he "unwittingly" took the substance.

The eight-time Grand Slam champion tells People that he felt it necessary to be as candid as possible in the memoir. New excerpts published Friday reveal Agassi wore a hairpiece that nearly fell off at the 1990 French Open, became jealous during ex-wife Brooke Shields' appearance on Friends, and how Shields put a photo of Steffi Graf— now married to Agassi — on the fridge for motivation to get in better shape before their wedding.