The tickets were part of a batch that were sent out by recorded delivery on Tuesday night.

While United did everything required of them, they have now been informed the tickets did not reach their destination and are now presumably heading onto the black market.

However, as the chip contained within the tickets has now been cancelled, they will not allow admittance to the Stadio Olimpico in Rome next Wednesday to see United tackle Barcelona.

United officials are now in discussion with UEFA to see what can be done on behalf of the unlucky supporters whose tickets have gone missing.

"The tickets that have gone missing are worthless, so we would repeat our advice for fans not to buy tickets from any unofficial source," said a United spokesman.

"We are now in discussion with UEFA as to what can be done for those supporters who have been affected."

UEFA will be under pressure to simply issue replacements, although given the security that will be in place around the stadium on match night and the limited timescale available, it might not be quite so simple.