Huge Chuck fan here, followed him from decently early on in his career. I don't think it can be argued against that Fedor is a fraction of the fighter he once was. Rocked and arguably beaten by Maldanado and hasn't looked good in years. (Decent vs Rizzo(Old as shit) Mir was 1 punch) So I'd say if Chuck, who I am sure is training on the daily, took his cardio seriously then there is no doubt that he'd probably have no chance and Fedor would win by KO