Keach, 67, is starring as former President Richard Nixon in the national touring production of Peter Morgan's celebrated play "Frost/Nixon."
The Center Theatre Group is presenting the stage drama at the Ahmanson Theatre in Los Angeles through March 29.
"Actor Stacy Keach has been diagnosed as having experienced a very mild stroke with no impairment whatsoever of his motor or speech abilities. He remains today in a Los Angeles hospital for observation and routine precautionary procedures," the company said in a statement issued to Playbill.com Wednesday. "The producers of 'Frost/Nixon' look forward to his speedy recovery and to his return to the show as soon as he is able."
Bob Ari, who understudied for Frank Langella -- the portrayer of Nixon in the Broadway production and in the subsequent film adaptation, is taking over the part until Keach returns, Playbill.com said.
Keach's Broadway credits include "Danton's Death," "The Country Wife," "The Caucasian Chalk Circle," "King Lear," "Indians," "Deathtrap," "Solitary Confinement" and "The Kentucky Cycle." He won a Golden Globe Award for his portrayal of the titular scribe in the TV miniseries "Hemingway," and played fictional private detective Mike Hammer on a television series and in several TV movies.