The New York Times reported the plan in a Wednesday story, citing unidentified network executives. The Hollywood Reporter had a March 1 report about a Fallon-Leno switch, which was denied by the network.
Looming over NBC is its messy, failed effort to replace Leno with Conan O'Brien, which ended in 2010 with Leno regaining "Tonight" and NBC losing O'Brien — who got a $45 million exit deal — to TBS. Leno's current "Tonight" contract expires in September 2014.
That occurred under a different regime, before NBCUniversal was taken over by Philadelphia-based Comcast Corp., which has a reputation for discipline. While NBC dithered and backtracked on its "Tonight" succession plan involving O'Brien, Comcast is likely to be more decisive.
"I don't know if it's possible to have a less orderly transition than Leno-O'Brien," said analyst Brad Adgate of media-buying firm Horizon Media.
Fallon contacted Leno in an effort to help smooth the potential switch, according to a Hollywood Reporter story Wednesday.
The latest roiling of the late-night waters began in January when ABC moved "Jimmy Kimmel Live" back to 11:35 p.m. Eastern to offer direct competition to Leno and CBS' David Letterman.
With the potential for Kimmel, 45, to draw advertiser-favored young viewers away from Leno (62) and Letterman (65), it's unsurprising that their networks might step up their succession planning.
At 38, Fallon is the youngest of the pack.
Leno, who took over "Tonight" from Johnny Carson in 1992, did not respond Wednesday to a request for comment. But he might be taking advantage of other ways to communicate — the "Tonight" stage and its audience of millions.
Although late-night hosts are known for needling their network bosses on-air, the timing of Leno's latest jabs at NBC seemed to make the network particularly uncomfortable. They reportedly asked him to stop; he hasn't.
"You know the whole legend of St. Patrick, right? St. Patrick drove all the snakes out of Ireland — and then they came to the United States and became NBC executives," Leno joked on Monday's show.
On Tuesday, he played off a news report about a Serbian woman with a rare brain condition that causes her to see the world upside down: "Isn't that crazy? It's unbelievable. She sees everything upside down. In fact, she thinks NBC is at the top of the ratings."
He kept up the pace Wednesday, according to a NBC transcript released after the show's taping and with gibe included. Leno quipped that scientists may be able to clone extinct species and bring them back from the dead, "so there's hope for NBC."
Leno, who briefly moved to prime-time to make room for O'Brien, has proved himself a wily survivor. Despite the challenge from Kimmel, he and "Tonight" have remained top-rated so far.
But if a change is destined, NBC could be eying next year's Winter Olympics in Sochi, Russia, as a premium launch pad for a revamped "Tonight," analyst Adgate said.
"If they're going to do it, it makes sense to do it when NBC is dominating television for 17 days," he said, and can heavily promote the "Tonight" switch. "They could have Fallon in Sochi, talking it up."
In the April issue of GQ magazine, "Late Night" producer Lorne Michaels ("Saturday Night Live") said a transition to Fallon had "an inevitability to it," adding that he was the closest to Carson that I've seen of this generation."