The star is making her Broadway debut at New York's Studio 54 Theatre.
She is expected to be ready for Thursday night's show, according to the Roundabout Theatre Company.
Last week Knightley's debut performance was interrupted by a man in the audience who shouted and threw flowers, before being escorted out by security.
He had been sitting in the mezzanine area of the audience before going to the railings to shout at the actress, who did not break character.
The man was heard to say, "Five seconds is too long to wait for a response!" before tossing the flowers on his way out. Other audience members claimed he had shouted: "We're going to be in heaven together."
Knightley plays the title character in Terese Raquin, a young woman in a loveless marriage who has a passionate affair. Based on the novel by Emile Zola, the "tale of love, lust, betrayal and guilt" also stars Gabriel Ebert.
The play is still in previews and is not due to officially open until the 29 October.
Although it is The Imitation Game and Pirates of the Caribbean star's Broadway debut, Knightley has appeared on the West End stage twice before. She stared in 2009 comedy The Misanthrope and Lillian Hellman's The Children's Hour in 2011.
British actress Keira Knightley was forced to cancel Wednesday night's performance of her Broadway show Therese Raquin due to a "minor injury".