Question marks over Russian tennis star Nikolay Davydenko were again raised yesterday when the world No 4 was involved in yet another contentious match.

Davydenko was soundly thrashed 6-2 6-2 by Marcos Baghdatis in the third round of the Paris Masters, and during the game he was asked to "try your best" by the umpire Cedric Mourier following a string of double faults. His opponent was disbelieving at the net questioning his opponent's motivation.

Trading exchange Betfair are currently refusing to trade on any match involving the Russian due to a pending ATP match-fixing investigation that focuses on a game in Poland in August against world No 87 Martin Vassallo Arguello when at one set all Davydenko withdrew with a foot injury - which triggered Betfair's action after they saw suspicious trading activity on the exchange.

Davydenko, who was the defending champion before yesterday's debacle made ten double faults and 36 unforced errors during a match he was 4/7 to win at the outset. When asked by the umpire to step up his performance Davydenko responded by saying "what can I do?" to which the French umpire replied: "Serve like me. If you serve like me, you put it in the box. That's it."

At last week's St Petersburg Open, Davydenko was fined $2,000 (£976) for not trying hard enough against Croat Marin Cilic yet he remains bemused at the allegations and puts his troubles down to a loss in form.

"I cannot serve," he said after the match. "That was happening in St Petersburg. I don't have pain really. I have no pain in my elbow. I need to find what's the reason I cannot really serve."

ATP president Etienne de Villiers told a conference in London yesterday that he would ban for life any player caught match-fixing.

"There is no excuse for that," he said. "You are undermining the integrity of the sport, you are destroying a level playing field. As far as we are concerned in tennis, if they are involved in match fixing they will be thrown out."

Former world No. 1 Martina Hingis announced her retirement from tennis yesterday, after she revealed that she had tested positive for cocaine during Wimbledon this year. The 27-year-old, winner of five Grand Slam titles, strenuously denied taking drugs, and has vowed to clear her name.