Doctors have advised Muggeridge not to risk racing

Muggeridge fractured a bone in his back while testing last month and has told to sit out the two races on 23 April.

"The injury is in a delicate position, and even if I don't feel any pain, a hard fall could make it much worse," said the Winston Honda rider.

His place will be taken by experienced Italian Giovanni Bussei, who returns after injury problems of his own.

Bussei said: "Of course I am sorry for Karl, I know how he is feeling at the moment. I honestly hope he will get well soon.

"I really hope to pay back the trust they gave me by bringing as many points as possible to the team."