The man, who was an avid St Pat’s fan, was found in his hotel room this morning.
A club statement this afternoon read: “It is with great sadness that St Patrick’s Athletic learned of the death of an English based fan of the club in Warsaw this morning.
“The club would like to express its deepest condolences to the fan’s family and friends on this very sad occasion.”
The club is not making any further comment.
It is understood that the deceased is an Englishman.
About 200 Saints fans are in Warsaw for tonight’s European game against the Polish champions at the Pepsi Arena.