WASPS' back row star Billy Vunipola has rejected a new contract and will leave the club this summer.
Vunipola, 20, has just been promoted to the England Saxons squad and is one of the club's most promising talents.
His decision to depart is a significant blow, and also a slight surprise after Joe Launchbury and Christian Wade did agree long-term deals.
Vunipola is now free to join his brother Mako at Saracens.
Wasps said: "The club has been informed this afternoon that Billy Vunipola has decided to leave at the end of the season.
"We are incredibly disappointed that he has chosen to leave and we will make a full comment on his departure tomorrow."
The only consolation for Wasps is that they are strong in the back row, with James Haskell, Ashley Johnson, Jonathan Poff, Sam Jones and Matt Everard all established.