
The serial joker has struck a number of times at the Premier League champions' Cobham training complex over the past 12 months.
The mystery slasher, thought to be a Chelsea player, can strike up to twice a week, according to a report in the News Of The World.
Chelsea and England midfielder Frank Lampard said: "It's gone on for about a year. We get in to find the bum cheeks cut out of our underpants.
"It has to be one of the players. They are the only ones with access. You might get two hits in a week, then he won't attack for a month or so."
Lampard added: "I've a good idea who it is but wouldn't dream of making accusations until I have proof.
"I hope it's soon - it's costing a fortune in designer underwear!"
A club insider told the paper: "It was a bit of a laugh but now the lads are a bit cheesed off.
"There's hardly any holes in our defence - so it's a shame the same can't be said of our underpants."

