Four-time Olympic show jumper Michael Whitaker has been suspended after his ride, Tackeray, failed a drug test.

The 49-year-old has been provisionally banned after the stallion tested positive for the synthetic hormone Altrenogest during a competition last month at La Baule, France.

Whitaker has requested his 'B' sample be tested. If that result is also positive, he will request a full hearing before an International Equestrian Federation tribunal.

Whitaker, a silver medalist at the 1984 Olympics, was a late withdrawal from last year's Beijing Games due to an injury to his horse, Portofino.

The equestrian world has been rocked by a series of doping cases in the past year, with six riders being suspended in Beijing, and Isabell Werth’s horse, Whisper, testing positive recently.