ATP Tour officials are investigating the fourth-ranked Davydenko's loss Thursday to the 87th-ranked Martin Vassallo Arguello of Argentina in which the Russian retired because of injury in the deciding set.

In an unprecedented move yesterday, British online gambling company Betfair voided all bets placed on the match, saying the market wasn't fair.

Betfair said it received about $7 million in bets on the match — 10 times the usual amount — and most of the money was on Arguello to win, even after Davydenko won the first set 6-2.

Eckhard Oehms, Davydenko's agent, denied the 26-year-old player had any connection to the betting.

"We've got nothing whatsoever to do with that," Oehms told The Associated Press by telephone today. "Neither Nikolay nor his coach nor me nor anybody out of our entourage has been involved in this.

"This is a matter that is important to us. We can't have his reputation being spotted by things like this."

Arguello won the second set 6-3 and was leading 2-1 in the third when Davydenko retired, saying he had aggravated a left foot injury in the second set. He received medical attention from a tournament trainer before deciding to quit.

The ATP says Davydenko officially retired from the match with tendinitis in his left big toe.

Oehms said Davydenko flew yesterday to Germany, where he received treatment on his foot at the University of Cologne Clinic. The player has since forwarded all the necessary medical reports to the ATP, Oehms said.

Oehms said Davydenko was "flabbergasted" when told about the suspicious gambling patterns.

"He said: 'What?'" Oehms said. "He's very outspoken, he's not scheming or hiding. He's a very plain, open person. He just couldn't get what this is.