The Houston Texans defensive end finished last season just two sacks short of Michael Strahan's record, having also made 81 tackles and four forced fumbles.
His teammate told the Inside the Huddle podcast: "The things that he's going to be able to accomplish are unbelievable. When you talk about the potential that he has of really being the greatest defensive player ever, he could be. I know that's very premature but he's that kind of player.
"I think if he just keeps doing what he's doing and obviously stays healthy, he's on that track. He's incredible. There's no other word for him.
"He's one of those guys that he's truly the best at what he does. Just the combination of speed, the power, how he plays, his endurance, his smarts, the scary part is it's his second year. He hasn't even hit his peak yet."
Watt was named the NFL's defensive player of the year in 2012.