From rubbing shoulders with some of the biggest names in sport, Gavin Hopper must now contemplate a jail sentence after the tennis coach and confidante was found guilty of nine sexual charges by an Australian court.

A former mentor to Grand Slam champions Monica Seles and Iva Majoli and leading men Mark Philippoussis and Tommy Haas, Hopper was late on Monday found guilty of charges relating to a teenage girl who attended a school where he taught.

The jury at the Victorian County Court found the 48-year-old guilty of three counts of indecent assault and six of gross indecency.

The woman, now 33, told the court she was a student at Wesley College when Hopper taught maths and physical education at the school. The four-year affair began in 1985, the court was told.

Hopper, a professor of sports science and author who now runs a tennis academy on Queensland's Gold Coast with Australia's 1987 Wimbledon champion Pat Cash, denied having a sexual relationship with the girl.

His lawyers have said they will appeal the decision.

Hopper, a married father of two girls aged 13 and nine, was remanded in custody for sentencing at a later date.