They believe taking care of his body will be Mahomes' big challenge if he is to emulate Brady over the course of his career.
Speaking exclusively to RadioTimes.com for The Big RT Interview, Bell said: "If we look at Patrick Mahomes, I expect this guy will be the greatest of all time if he can play and have that kind of longevity.
"As an athlete, I'm just enamoured by the fact that guys can play that long and what they do to take care of themselves. That's Mahomes' challenge.
"I am leaning Kansas City just because I gotta see Patrick Mahomes double it up. I just want that to happen."
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Umenyiora added: "Look at this guy's career trajectory. If you take away the longevity of a Tom Brady, there's no telling how high this guy can go.
"If he's able to play for 15 years, you're probably gonna see him own a majority of the records in NFL history.
"I mean, just a dynamic football player, a guy with the kind of talent that we rarely see coming to the NFL.
"One thing that impresses me the most about Mahomes is, this is a guy who's never lost an NFL football game by more than one score, it's only happened to him in college.
"In his entire NFL career, he has never lost the game by more than one score. And this means that as long as this guy's on your football team, you have a chance to be in every single game. It's just amazing what this guy is able to do."
Super Bowl LV is live on BBC One and BBC Radio 5 Live on Sunday 7th February with kick-off at 11:30pm
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