Novak Djokovic, the world No3, claims he was offered £110,000 to lose in the first round of a tournament in St Petersburg last year.

The 20-year-old Serb flatly refused the offer and did not even attend the tournament. There is no suggestion that the organisers of the tournament were involved although the ATP is focusing its investigations in Russia and Ukraine.

The revelation comes after the just retired Tim Henman warned the authorities to be "very vigilant" about the dangers of gambling in tennis. "I personally have never experienced it but, listening to the players talking, it seems it goes on," the former British No1 said. "Tennis doesn't want to be associated with that."