Exclusive Wimbledon passes reportedly sold on internet auction site eBay for £3,000 were probably fakes, the All England Club says.
Fans have begun queuing ahead of Monday's opening games
The passes, promising access to areas reserved for players, were bought before the sale could be stopped.
The tennis club has already taken out several injunctions stopping vendors from selling genuine tickets onwards.
Fans have started queueing outside the southwest London venue, hoping to see the first day's play on Monday.
About 500 tickets are sold at the turnstiles on the day for Centre Court and Courts One and Two.
The club allows only debenture tickets to be transferred, and warned any people who bought other tickets that they would be turned away.
Debenture tickets are issued for five years and entitle the holder to seats on centre court on each day of the tournament during that period.
"We don't think the passes existed but they were advertised as such," an All England Club spokesman said.
"We think this was probably a fraudulent attempt.
"Our general view on eBay is that we're not keen on it. If they're debenture tickets that's fine but anything else we're definitely not keen.
"It's not going to work and that's the big problem for the buyers - they will not get in."
EBay said fake tickets would be removed if spotted.
"It is against eBay's policy to allow fraudulent or stolen goods and we encourage the community to report any suspicious items to customer services," a spokeswoman said.
"They will then be investigated and withdrawn if they are fraudulent."