There is match-fixing in tennis says British No.1 Andy MurrayAndy Murray today sensationally claimed that tennis is "fixed" and that everyone on the professional circuit knows matches are being affected by gambling.He said: "It's pretty disappointing for all the players but everyone knows it goes on."The sport has been tainted by controversy in recent weeks with the ATP, the men's tour's governing body, investigating betting patterns concerning a match in Poland between Nikolay Davydenko and Martin Vassallo Arguello.The Russian's price drifted out despite him winning the first set and he later pulled out of the match due to injury, although Davydenko denies any wrongdoing.Novak Djokovic recently claimed he was offered a £110,000 bribe to lose a first-round match in St Petersburg while journeyman Belgian Gilles Elseneer revealed that he rejected an offer of £70,000 to throw a match at Wimbledon in 2005.With horse racing currently being dragged through the mire by the start of the Kieren Fallon race-fixing trial, Murray now fears tennis is at risk as the temptation to cheat is too great for players struggling at the lower end of the circuit.Speaking ahead of the Kremlin Cup, in Moscow, he added: "It doesn't surprise me. Some guys come to tournaments like this every single week and the first-round loser's cheque is sort of €2,500 and they have got to pay for their air fares and, you know, it's only a 10 or 12-year career so you have to make all your money while you're still playing."But the British No1 told Radio Five Live he feels the nature of the sport makes it difficult to prove when someone is trying to engineer an outcome.Murray admitted: "It's difficult to prove because they can try their best until the last couple of games of each set and then make some mistakes, a couple of double faults, and that's it."