Cox said the Blues coach had approached him about continuing his stellar 290-game career in Melbourne, but the 33-year-old ultimately decided his body would not allow it.
"I did speak to Mick and he asked if I wanted to play on for another season," Cox told Adelaide radio station 5AA.
"For me, the decision was made. Not being able to do what I wanted to do on the football field for a period of time, the decision was quite easy.
"We had a really good chat about my future and obviously my coaching aspirations."
Instead of joining former teammate Chris Judd at Carlton, Cox stayed with the Eagles to become their ruck coach.
The six time All Australian believes the extra travel WA-based footballers have to endure means it is unlikely they will play past 30.
"Recovery's a massive part of that and I suppose you notice that when you play Fremantle and you have a couple of games in a row at home - you can actually get more training load in throughout the week not having to recover from a flight or prepare for a flight," Cox said.
"I think it just catches up with you really quickly; the older you get, the longer it takes to recover.
"And if it's every second week going on a plane for four hours, plus a bus trip, plus layover time, waiting for your bag, it turns out to be a long night when you get home."
In his coaching role, Cox will work closely with former ruck teammates Nic Naitanui and Scott Lycett, as well as providing plenty of experience for the club's young players.
"For the past couple of years coaching has always been an avenue I've wanted to go down," Cox said.
"I suppose I’ve learnt so much over my footy career, if I could pass on that knowledge onto some younger kids and fast-track their development, then great."
