Fallon "is the best and no matter who CBS puts in that place, I think he'll still be the best," NBC Universal CEO Steve Burke said.
The NBC chief said he didn't think Tina Fey or Jay Leno, two people with NBC ties who have been mentioned as potential Letterman replacements, would be in the running. Fey seems happy making movies and shows for NBC, Burke said. Fey, who made and starred in "30 Rock," has a production deal with NBC.
Former "Tonight" host Leno is still talking with NBC about a deal where he will do occasional specials, he said.
Fallon has topped the late-night ratings since taking over for Leno in February, and is particularly strong among the young audience NBC seeks. While the network was always confident in Fallon, Burke said the new host has easily exceeded expectations, and is even bringing viewers back to the 11:30 p.m. time slot.
"He has turned out to be, I think, exactly what America is looking for," Burke said.
Burke said he and his wife had dinner with Fallon during the Vancouver Olympics four years ago and left telling his wife that Fallon was someone who would be running the "Tonight" show someday. And as CEO at NBC Universal, Burke was in the position to make it happen.
"He is very unique," he said. "Whoever ends up doing the job at CBS, we wish them well. We think we'll do fine."
CBS was not talking Monday about candidates to replace Letterman, which have ranged from Stephen Colbert to Conan O'Brien to Neil Patrick Harris. The network isn't giving a timetable for when a selection will be made, and a day hasn't been for Letterman's last show, either.
Harris, an actor in the just-concluded CBS show "How I Met Your Mother" and a Tony Awards host for CBS, said Monday he hasn't had any talks about filling Letterman's chair. He is preparing for a return to Broadway in "Hedwig and the Angry Inch."
"I'm super-focused on 'Hedwig' at the moment, so that hasn't even been a conversation at all," he said. "But I'm a big fan of CBS and (CBS Corp. chief) Les (Moonves), so who knows? It would be an asinine amount of work."
John Oliver, who is preparing for the debut of his HBO comedy series this month, said in an interview with The Associated Press that he had informal talks with CBS last year, but Letterman's job wasn't mentioned.
"I'm pretty mortified that he's leaving," Oliver said. "He was a pretty big deal to me."
AP Drama Writer Mark Kennedy contributed to this report.