The actor Ian McKellen was hospitalized but expected to recover quickly after falling off the stage during a performance of “Player Kings” at a theater in the West End in London on Monday night, the producers of the play said.

After a scan, doctors at Britain’s National Health Service said that McKellen would “make a speedy and full recovery, and Ian is in good spirits,” according to a statement by the producers.

In a statement provided by his publicist on Tuesday, McKellen thanked the N.H.S. professionals who treated him. “To them, of course, I am hugely indebted. They have assured me that my recovery will be complete and speedy and I am looking forward to returning to work,” he said.

McKellen, 85, who has been nominated for two Academy Awards and has won a Tony, a Golden Globe and multiple Olivier Awards, is starring in the play, an adaptation of William Shakespeare’s two “Henry IV” plays, directed by Robert Icke. McKellen plays John Falstaff, a fictional character who appears in three Shakespeare plays.

The fall took place during a battle scene, according to Aleks Phillips, a BBC journalist who was in the audience on Monday night and described what he saw in an article.

“It happened so quickly that at first it appeared to be part of the performance,” Phillips wrote. “But the actor cried out and staff rushed to help.”

After the fall, the performance was canceled and the audience left the theater. Tuesday night’s show was also canceled, the producers said, but McKellen was expected to return to the stage for a matinee performance on Wednesday.

McKellen has often returned to the stage for Shakespeare plays throughout his six-decade career, including in recent years as King Lear and as an octogenarian Hamlet. He is also a fixture of the silver screen, including his roles as Gandalf in the “Lord of the Rings” and “Hobbit” movies, as well as Magneto in the “X-Men” series.

“Player Kings” is in its final week and runs at the Noël Coward Theater through Sunday.