Germany's respected Suddeutsche Zeitung reported that Spyros Marangos had said he had evidence that certain UEFA representatives were corrupted in the bidding process in 2007, when Italy and a joint Croatia and Hungary bid missed out.
"In relation to this as yet unsubstantiated claim UEFA wishes to state that, as always, it can only open an investigation on the basis of tangible elements of proof," a UEFA statement read.
"To date these have never been provided to UEFA by this individual prior to any meeting and this in spite of repeated requests by Europe's governing football body.
"UEFA has therefore today, via its legal counsel, again requested the said individual to submit to UEFA any evidence that according to him should confirm his allegations, by Wednesday 27 October at the latest."
Bid processes for soccer tournaments have recently come under scrutiny with world governing body FIFA provisionally suspending two members of its executive committee on suspicion of selling their votes to host the 2018 and 2022 World Cups.
"THAT'S NONSENSE"
UEFA added that in its case legal action would be considered against the individual if evidence was not forthcoming.
Marangos, who could not be reached for immediate comment, was not named in UEFA's statement.
Ukraine's Deputy Prime Minister Borys Kolesnikov, in charge of the country's planning for Euro 2012, denied wrongdoing.
"These allegations are three years old. If they were at least partly true we wouldn't have any championship," he was quoted as saying by Interfax news agency.
Polish officials were even more forthright.
"This is just slander, it's not even worth talking about," said Polish Sports Ministry spokesman Jakub Kwiatkowski.
"We are not treating it seriously, as there is no proof presented. By this logic anyone could walk around talking whatever, that's nonsense."
A spokeswoman for Poland's FA said it would be contacting UEFA to request clarification over "groundless" accusations and reserved the right to take legal action.
