Australian boxer Bianca Elmir failed a doping test and was slapped with a provisional ban that threatens her chances of competing at the London Olympics, her coach told Australian media on Wednesday.

Elmir, Australia's flyweight champion and Oceania's bantamweight champion, tested positive for a banned diuretic at the national titles in Tasmania in February, her coach Garry Hamilton told the Sydney Morning Herald.

Hamilton said 30-year-old Elmir had taken a tablet before the national titles to treat "swollen ankles" on a long-haul flight.