Sir Ian McKellen has been taken to hospital after falling off stage during a performance of Player Kings at the Noël Coward theatre in London.
The actor, 85, was in a fight scene when he lost his footing and fell.
A theatre spokesman said later that he was in “good spirits” and expected to “make a speedy and full recovery”.
He is expected to be back on stage next Wednesday for a matinee performance of the play.
The audience was evacuated from the theatre and informed that the evening show had been cancelled.
Player Kings is a production of Henry IV, Parts One and Two, and started its 12-week West End run in April.
Sir Ian – who plays John Falstaff – had been circling a battle scene involving the Prince of Wales and Henry Percy when he fell off the front of the stage. The actor cried out and staff rushed to help.
He has had a scan and is expected to make a full recovery, a spokesperson for the theatre told the PA news agency.
Next Tuesday’s performance of the play has been cancelled “so that Ian can rest”, the spokesperson added, but the actor is expected back the following day.
The spokesperson also thanked doctors Rachel and Lee who were “on hand in the audience” and staff at the venue for their support.
Sir Ian’s previous Shakespeare credits include roles as Richard II, Coriolanus, Iago, Richard III, King Lear and Macbeth. He is also set to star as Hamlet, in a new film adaptation directed by Sean Mathias.
His on-screen credits include Gandalf in the Lord of the Rings and Hobbit trilogies, and Magneto in the X-Men movies, as well as roles in Beauty and the Beast, The Da Vinci Code and Mr Holmes.
The actor also appeared in 10 episodes of the ITV soap Coronation Street as the scheming romance author Mel Hutchwright.
Five years ago, Sir Ian was forced to cancel a King Lear showing at London’s Duke of York theatre after sustaining a leg injury while running to catch a train, but ensured the audience was in for a good time, by sitting on stage and answering questions.