"It's just a matter of when," Manning told NOLA.com on Friday during the Manning Passing Academy in Thibodaux, Louisiana.
"Obviously, he's just been the ultimate pro, taking care of himself, being in great shape. Credit to him for playing as long as he has at such a high level," Manning continued. "He's just been a great model of consistency, what he and Sean [Payton] have been able to do together for  years now."
Manning retired after the 2015 season with 71,940 career passing yards and 539 touchdown passes -- both all-time NFL marks.
But Brees, 39, needs just 1,496 yards to pass Manning -- which should take him five or six more games. As Brees pointed out recently, "There's a reason they put [the Saints' Week 5 game] on Monday night. I don't think any of us are dummies."
It will take Brees a little bit longer to break Manning's touchdown record. Brees is still 51 TD passes behind Manning -- so he won't get there until 2019 at the earliest.
Manning told NOLA.com that the TD mark "probably has a little bit more meaning for a quarterback, because it means you got six points and you're doing something good for your team. ... Yards, as you all know, can be a little bit misleading because it doesn't necessarily mean winning games."
"I know Drew feels the same way -- you never play for individual records," Manning said. "Drew has been the ultimate team player. It's all about helping your team win. I know when he breaks any of these records, it's not going to mean as much to him if the Saints don't win the game that day."