The Belgian stopper has moved to Vicarage Road on a one month loan deal.
"We're grateful to Chelsea for providing us with goalkeeping cover," said Hornets boss Adrain Boothroyd.
"We're grateful to Chelsea for providing us with goalkeeping cover," said Hornets boss Adrain Boothroyd.
"We've got Yves for a month, so we can see how he shapes up in training and call on him if we need his services."