Manchester United's Casemiro celebrates with fans during the Europa League semifinal second leg soccer match between Manchester United and Athletic Bilbao in Manchester, Britain. (AP )

BILBAO, Spain, May 19 (AP): With tens of thousands of fans of Manchester United and Tottenham expected in Bilbao this week for the Europa League final, UEFA warned them Monday about buying unauthorized tickets, which should not get them into the stadium.

Both clubs, which have huge fan bases, were allocated 15,000 tickets in the 50,000-capacity venue, with some priced at just 40 euros ($45). Those numbers are typical for a Europa League final.

Prices in the thousands of euros (dollars) have been demanded on secondary ticketing websites, and UEFA said buyers could be refused entry on Wednesday at Athletic Bilbao’s stadium.

"Such tickets may be canceled by UEFA at any time, and fans are likely to be refused entry or be ejected from the stadium,” the European soccer body said in a statement.

"In addition, fans may not receive the tickets which they have purchased from these unauthorized third parties,” UEFA said, specifying "websites, agencies, touts” as problematic sellers.

UEFA also sold about 11,000 tickets in a global sale through its website, and nearly 9,000 were retained for sponsors, broadcasters, European soccer federations, and guests.

All tickets were distributed digitally with security features in a UEFA ticketing app for cellphones designed to prevent the buyer from transferring them.

"Only the phone used to download the mobile tickets will be able to access the stadium,” UEFA warned. "Screenshots of mobile tickets are not valid tickets.”

UEFA typically chooses venues for European club competition finals at least two years in advance, and has long faced criticism it regards as unrealistic for not switching stadiums to suit the two teams. Those teams advance through semifinals played just two or three weeks before the final.