"The things that he's going to be able to accomplish are unbelievable," Cushing told ESPN.com's John Clayton last week in his "Inside The Huddle" podcast. "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."
Watt, 24, had a dominating season in 2012, leading the NFL with 20.5 sacks despite having to play with an elbow injury that he revealed this week was more significant than thought.
Besides his league-leading sack total, he also deflected 16 passes, made 81 tackles and forced four fumbles.
"He's incredible. There's no other word for him," said Cushing, who added that it's usually hard for him to give other players credit.
"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," Cushing said.