Seinfeld, whose iconic sitcom aired on the network during the '90s and '00s, praised NBC's vision in moving Leno to prime time, even if the gamble didn't quite work out as planned.
"This was the right idea at the wrong time," Seinfeld said while promoting his new reality show, "The Marriage Ref," in Los Angeles on Sunday. "I'm proud that NBC had the guts to try something."
Seinfeld also said O'Brien, who would be bumped from his current time slot at 11:35 p.m. ET, will emerge from the wreckage unscathed.
"What did the network do to him?" Seinfeld asked. "I don't think anyone's preventing people from watching Conan. Once they give you the cameras, it's on you. I can't blame NBC for having to move things around. I hope Conan stays, I think he's terrific. But there's no rules in show business, there's no refs."
It remains to be seen if O'Brien will stay with the network that made him a star of if he'll fly the coop. He could potentially move his schtick to a competing network or leave the late-night game altogether. According to The Wall Street Journal, O'Brien is exploring his options with Fox.
Amid sinking ratings and worried affiliates, NBC announced Sunday that the Jay Leno prime-time experiment will end Feb. 12.
NBC confirmed it will yank the comic's 10 p.m. nightly hour once the Winter Olympics begin, and it hopes he will accept a half-hour version of his show at his old time -- 11:35 p.m. -- instead.
"While it was performing at acceptable levels for the network, it did not meet our affiliates' needs and we realized we had to make a change," NBC Universal Television Entertainment Chairman Jeff Gaspin said at the NBC winter press tour in Pasadena, Calif., Sunday.
"What happened starting in November [was] the affiliates called, saying, 'Wow, wow, our local news is being affected more than we expected,'" Gaspin said.
NBC has spoken to Leno, Conan O'Brien and Jimmy Fallon about moving their shows to later start times, Gaspin said. Under the proposal, O'Brien, the man who replaced Leno as host of "The Tonight Show," would move to 12:05 a.m., and Fallon to 1:05 a.m.
"My goal right now is to keep Jay, Conan and Jimmy as part of our late-night lineup," Gaspin said. "As much as I would like to tell you we have a done deal, we know that's not true. The talks are still ongoing."
NBC said its stars were given the weekend to think about it. The network doesn't know whether O'Brien will accept a half-hour demotion or bolt to another network.
"What we're hearing from inside the Conan camp is they're kind of 50-50 right now with what they're going to do," said Mike Schneider, TV editor for Variety. "I mean, this obviously is a big smack in the face."
Last week, amid a firestorm of speculation that NBC might can O'Brien altogether, the network released a statement this week declaring its loyalty to the late-night comic.
"We remain committed to keeping Conan O'Brien on NBC," the network said in a statement Thursday evening. "He is a valued part of our late-night lineup, as he has been for more than 16 years, and is one of the most respected entertainers on television."
His Sept. 14 debut attracted 18.4 million viewers. By the second week, however, the number of viewers had dipped as low as 5.1 million.
A fall repeat of CBS's "CSI-Miami" topped Leno on a Monday night; not a good sign because Leno vowed this summer to beat the competing networks whenever they aired reruns. Before that, the FX series "Sons of Anarchy" was the first cable show to beat Leno.
Then there's the so-called Leno effect that has some of NBC's more than 200 affiliates grumbling that the show's weak lead-in is eroding audiences for their 11 p.m. newscasts. O'Brien's and Fallon's numbers for their late-night shows are also down, ostensibly because of a weaker Leno.
Leno made it clear in a 2009 interview with Broadcasting & Cable magazine that he wasn't ready to concede the fight.
"I enjoy being the underdog," Leno said. "Do I enjoy the battle? Yes, I get a certain amount of satisfaction from pounding my head against the wall.
"Emotionally, I can take body shots all day long and that doesn't really bother me," he added.
But in the end, bowing out of the 10 p.m. race wasn't a choice left up to him.
ABC News' Luchina Fisher and Michael S. James contributed to this report.