Players at all 92 league clubs were warned earlier this season to blow the whistle if they are approached about illegal betting or match-fixing, according to Professional Footballers' Association chief executive Gordon Taylor.
Advisers from the PFA visited every club and the dangers of becoming involved in such activities were spelled out clearly. It comes after Liverpool insisted they have had no contact from Europol or any other body in connection with match-fixing allegations against 2009 Champions League opponents Debrecen.
PFA boss Taylor said the issue of match-fixing was "very high on our agenda", and he said: "At the beginning of the season we had a team going out to all the clubs telling the players there should be no betting on any competition they have any association with, and that any approaches should be reported to the authorities."
The European law enforcement agency said one Champions League match played in England is under investigation - and according to Danish newspaper Ekstra Bladet, Europol sources said they are looking at Hungarian side Debrecen who lost 1-0 to Liverpool at Anfield in 2009.
There is no suggestion that anyone at Liverpool was involved in any wrongdoing.
Taylor added: "We have had some problems with one or two games in the recent past where players at Accrington Stanley and Bury were charged and sanctioned, so although it is not commonplace in our country we are not complacent or naive.
"We need to be vigilant at all levels of the game."
The Europol investigation is centred on the Debrecen keeper Vukasin Poleksic, according to Ekstra Bladet, who in 2010 was banned for two years by UEFA for failing to report an approach to fix matches for a betting syndicate.
But a Liverpool spokesman told Press Association Sport: "We have had no contact from Europol or any other organisation over this."
Debrecen said they will not respond to the allegations and a statement on the Hungarian club's website read: "Neither DVSC or the player wants to react to this news. Everything on this matter has been dealt with in 2010."