He's been under the spotlight since his teenage years, so questions about his legacy or having to answer them on a swaying boat weren't likely to toss the 37-year-old about.
But standing between Manning and his second Super Bowl ring is the NFL's No. 1-ranked defense. And like it or not, embrace the argument or point out its futility, a loss to Seattle is sure to damage the case for Manning.
"I've been asked about my legacy since I was 25 years old, which I'm not sure you can have a legacy when you are 25 years old, or even 37," Manning said. "I thought you had to be 70 to have a legacy. I'm not 100 percent sure what the word even means."
John Elway has a pretty good idea. The Hall of Fame quarterback, who also belongs in the conversation of greatest ever, faced the same questions about legacy when he lost in his first three Super Bowl appearances and didn't return until his 15th season.
But Elway, who returned to the Broncos as an executive in 2011 and was instrumental in bringing Manning to Denver a year later, needed to win the first one to settle any debate. Manning already won a Super Bowl with the Colts in 2007, in his 10th season.
Elway and the Broncos beat the Packers, 31-24, in 1997. And when they followed it up by topping the Falcons, 34-19, the next season, the soon-to-be-retired quarterback's legacy was cemented.
He was one of the greatest modern-day quarterbacks to ever play, joining Johnny Unitas, Joe Montana, and Dan Marino, according to most. But Manning has a chance to eclipse them all, even his generational counterpart, Tom Brady.
"I think that when people say that, they're looking for something," Elway said last week. "Because he had such a tremendous year, I mean, what else are you going to talk about Peyton Manning that's negative other than, 'OK, we've got to go to his legacy.' So I don't think this game, one way or the other, affects his legacy."
Even if Manning never won a playoff game he would be in the argument based on his regular-season numbers alone. He's second to only Brett Favre in career passing yards (64,964) and touchdowns (491) and behind only Aaron Rodgers in passer rating (97.2).
Manning's regular-season winning percentage (.696) is third behind only Brady (.775) and Montana (.713) among modern-era quarterbacks.
But his postseason numbers have paled in comparison.
"He's almost a victim of his own success," said Terrell Davis, a former Broncos running back and Elway teammate. "You look at Peyton Manning's career numbers regular season, and they're mind-boggling. But you turn the page at his postseason stuff - it doesn't weigh out the way we think it should weigh out."
The postseason passing yards per game are higher than his regular-season numbers (286.8 to 270.7), and the completion percentage (64.0 to 65.5) is only slightly lower. But his touchdown-interception ratio (1.64 to 2.24) and winning percentage (.500 to .696) are noticeably worse.
Football is, of course, a team game. Too often, quarterbacks are judged based on wins and losses. But if we're going there, Montana has won four in four opportunities, Terry Bradshaw four in four, Brady three in five, Troy Aikman three in three, and Elway two in five.
With a win, Manning would have won two in three and equal Roger Staubach; Bart Starr; his brother Eli; and Elway in Super Bowl titles.
Kurt Warner won one Super Bowl in three appearances.
"I could be 3-0 because I've lost two Super Bowls in the last minute of the game," Warner said. "I could be 0-3 because the one I won we stopped the guy on the 1-yard line. Or I could be anywhere in between. And I don't believe that [having] won or lost the ones that I did changed anything about who I was as a quarterback."
To Warner, Super Bowl appearances mean more than wins. That's why, he said, Brady's and Elway's five were so impressive.
"But I believe, big picture, if we're talking best quarterback to ever play this game, I believe when other guys have four, [Manning] probably has to have more than one to be considered in that narrative," Warner said, "whether it's fair or not."
Former Ravens coach Brian Billick, who won a Super Bowl in 2001, said that Manning's winning two Super Bowls with different teams could be considered as notable as Brady's three Lombardi Trophies.
"The Tom Brady contingent says, 'Aw, he's got three Super Bowls.' Yeah, but [Manning would have] two with two different teams," Billick said.
Davis said that he thought Manning's winning with two different teams would be more impressive than Brady's three. Manning is already only the third quarterback to reach the Super Bowl with two different teams, and he, of course, knew the first two when quizzed last week.
"I can name them. Do you want me to help you with the answer?" Manning said to laughter. "Warner and Craig Morton were the two. I saw Kurt this week. Craig Morton did it with Denver and Dallas. That to me is a special accomplishment in itself."
It's special, Manning said, because of where he was just two years ago. He missed the entire 2011 season with the Colts because of two neck surgeries. Doctors were unsure if he'd ever play football again.
The uncertainty and the Colts' No. 1 draft slot, which they would eventually expend on quarterback Andrew Luck, led to a parting of the ways with Manning. Several teams tried to sign him as a free agent, but he ultimately opted for the Broncos.
Elway's sales pitch and his having been there and done that certainly played a part in the decision.
"I think that relationship definitely helped," Elway said. "I would [have] liked to have somebody that had been in the position running an organization when I was playing quarterback too that had the same mind-set.
"I have never really talked to him about exactly why he chose Denver, but I have a feeling that that was part of the decision."
And now they have the opportunity to win together and make history - Manning for the second time and the first quarterback to do so with two teams and Elway the first as a quarterback and team executive.
"He's going to be one of the all-time greats no matter what, and this will definitely help [the argument against that] if we lose it," Elway said. "But the bottom line, this year that he has had - legacies don't get great until you're done. That's when people start talking."
And Manning doesn't sound close to done. He said last week that he wanted to continue playing beyond this year.
"This legacy question keeps popping up, and I guess I had a little more time to think about it," Manning said. "If I had my choice, what my legacy would be, would be that I played my butt off for every team that I ever played on, I was a really good teammate, and I did everything I could to win."