Davydenko cleared of match-fixing in key betting probe

The 27-year-old Russian lost to Martin Vassallo Arguello at the Polish Open in Sopot last August, retiring injured at 6-2, 3-6, 1-2 in the second round match which attracted nearly $7million (£3.5m) in wagers on Betfair.

The online betting company took the unprecedented step of voiding all bets because of highly-irregular gambling patterns.

Davydenko, who is due to meet Andy Murray at the current Sony Ericsson Open Masters series event in Miami, was known to be carrying a foot injury when he faced Vassallo Arguello.

He started at an innocent looking 5-1 on, but what aroused suspicion is that, after winning the first set, he had drifted to 4-1 against. His retirement came after he was treated on court for the foot injury.

Sportsmail understands that the independent experts who were brought in by the ATP Tour are continuing to look into the conduct of Vassallo Arguello.

While there has been some frustration among the British investigators at the manouevrings of World No 4 Davydenko's legal team since last summer, what they have seen of his phone and bank records and in the course of interviews has been far from conclusive.

One problem that has emerged in looking into the whole issue is the legal framing of regulations and obligations for players, and one outcome of the current review is expected to be the rewriting of contracts and rules relating to gambling activity.

At least 15 male players have reported that they had been approached to fix matches and several lesser-known Italian players have been punished for betting on matches, although none of the game's better-known stars have been implicated, bar the Russian.

It is believed that since a more robust approach was taken by the authorities, questionable activity among players and their associates has been substantially reduced, although one men's singles match in the past month has attracted scrutiny.

A new concern that has emerged in recent months is that of people trying to gain a split-second advantage ahead of television pictures by being at the match.

Two spectators were thrown out of a women's event in Antwerp for suspicious use of laptops, while another was expelled from the recent tournament in Dubai after being caught giving a commentary via mobile phone.

The Tennis Integrity Unit are due to present their findings into match-fixing during the French Open at the end of May.

But what exactly happened at Sopot may forever remain a mystery.