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John Fahey, the head of the World Anti-Doping Agency, Wada, wants the tennis authorities to explain Andre Agassi's admission that he used a banned drug, crystal methamphetamine, in 1997 and escaped a suspension by blaming his positive test on a spiked drink.

Agassi, an eight-times grand slam champion, and one of only six male players to have won all four majors, writes in Open, his autobiography, that he was introduced to crystal meth by his assistant "Slim" at a time when his form was falling and he was having doubts about his impending marriage to the actress Brooke Shields.