Ibrahimovic was superb in his debut season for United but a serious knee injury towards the back end of that campaign stopped him in his tracks.
He stayed at United without picking up a wage and was intent on winning his place back in the team but failed to do so and ended up joining LA Galaxy in March.
“I was thankful for what the club did for me and what Jose Mourinho did for me," Ibrahimovic told BBC Sport.
“I told the club I don't want any salary, you keep it and I'll stay. Just give me the opportunity to train here.
“They had a Zlatan before and after I was not ready to give them the same Zlatan."