People.com: Even in the hospital Jay Leno hasn't lost his sense of humor.

The Tonight Show host, 58, canceled the taping of his talk show and checked into Providence Saint Joseph's Medical Center in Burbank on Thursday. No information has been released on the nature of the funnyman's ailment, but a rep for the show says he's "doing just fine."

"He was kidding around with the hospital staff and running his monologue jokes by the doctors and the nurses," says NBC's Tracy St. Pierre. "He's expected back to work on Monday."

According to sources, Leno, who rarely calls in sick and is famous for his strong work ethic, "was just not feeling well. Somebody from the show drove him over to the hospital."

Actor Ryan Reynolds - as well as an animal handler and several reptiles - had been scheduled to appear on the show.

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