David Tennant is having surgery on his back on Thursday, and won't be able to appear on stage until after Christmas.
The Doctor Who actor was said to be "gutted" when he had to pull out of the Shakespeare play Hamlet on Monday night because of problems with his back.
Tennant said he was really disappointed he would have to miss even more shows.
He said: "My back problem has progressed to the point where it is currently impossible for me to carry on without surgery."
Tennant is being replaced by an actor called Edward Bennett, who normally plays another part in the play.
David Tennant as Hamlet
Bennett received standing ovations from the audience when he played Hamlet on Monday and Tuesday.
Tennant said: "I want to get back on stage as quickly as possible, and I am very grateful to Ed who has courageously got to grips with the role, but in a much shorter time.
"It's a fantastic achievement."
Artistic Director Michael Boyd said: "We all wish David a speedy recovery."