Jimmy Kimmel and George Clooney put on an 'ER' reunion - and Hugh Laurie showed up

What happens when a late-night host plans a show reunion and only one actor from the old series shows up? That's the dilemma Jimmy Kimmel dealt with on Tuesday night with George Clooney.

With Clooney stopping by to promote his new movie, "Hail, Caesar!" Kimmel went into a commercial break teasing a proper "ER" reunion. What a difference a few ads make. 

As the "ER" sketch is underway, Clooney requests a scalpel, and then Kimmel breaks the news.

"I know I'm supposed to be under," Kimmel, playing a patient, says to the star. "The reason nobody is bringing you a scalpel is this is kind of a last-minute thing, and we had some trouble getting the whole cast of 'ER' together."

He then explains why everyone couldn't make it: Julianne Marguiles was shooting "The Good Wife," Noah Wyle had "Taco Tuesdays" with his family, Eriq La Salle had jury duty, Sherry Stringfield couldn't get an Uber, and Anthony Edwards is at SoulCycle.

The movie star is a good sport: "If George Clooney says he's going to show up for an 'ER' reunion, George Clooney does it," Clooney confirms.

The show reunion must go on, but Clooney won't go it alone. He appears alongside another popular TV doctor, "House" star Hugh Laurie. They save patient Kimmel's life with a pretty extreme medical technique.

Here's a hint:

Watch the video below: