Manchester United has posted a message on its website explaining that its players do not belong to online social networks. It advises users to treat any profiles in the names of its players with "extreme scepticism".
The club says this is because of the high numbers of people impersonating team members online.
"We don't want to stop players doing what they like within reason in their spare time," a Manchester United spokesperson told BBC News.
"But we do advise our players - especially the young lads - to be careful."
Manchester United players Wayne Rooney, Ryan Giggs and Darren Fletcher are believed to have had genuine accounts on Twitter, which are now closed.
"It wouldn't have been us who stopped them," said the spokesperson.
