Didn't Collins receive clearance from his doctor?
IIRC, Yes.
Andrew Brandt I believe wrote an article about how players physicians often will clear and/or sugarcoat medical record reports to make the player as shiny and healthy as they can.
It doesn't mean diddly unless that players own team physician clears him. Collins issue was the level of fusion (higher, the worse it is). No other team doc would clear him either.
And while they play different positions, Collins was by far the superior NFL player. Had that dude stayed healthy, MM thought he would have been a HOF.