Comparing injuries 50 years ago versus today doesn't work with how much medical science has changed. Heck 30-40 years ago a torn ACL was a career ending injury and now it's almost the norm at this phase. CMC is 25yrs old and had a rough couple years, the dude is a flat out baller. I'd have no prob with a cap restructure and giving up a 3rd.
Here's his (minor) injury history
Oct 8, 2016 - Non NFL - Inguinal Hip Pull - McCaffrey missed 1 game (vs. Notre Dame).
Sep 20, 2020 - Pedal Ankle (high) Sprain Grade 3 - McCaffrey suffered a right high-ankle sprain during Week 2's loss to the Buccaneers and missed six games
Nov 8, 2020 - Shoulder A/C Joint Sprain - McCaffrey injured his shoulder on the last drive of Week 9's loss to the Chiefs. He missed 4 games
Dec 9, 2020 - Thigh Glute Strain - McCaffrey's thigh tightened up ahead of Week 14 game. He missed 4 games due to that injury.
Sep 23, 2021 - Thigh Hamstring Strain Grade 2 - McCaffrey suffered a strained hamstring in Week 3's Panthers win over the Texans. He missed five games.
Nov 28, 2021- Pedal Ankle Sprain Grade 2 - McCaffrey rolled his left ankle in Week 12's loss to the Dolphins. He was placed on injured reserve Monday and has been ruled out for the remainder of the season.
Source - https://www.draftsharks.com/fantasy/injury-history/christian-mccaffrey/7750