An interview with MUTV in which he was critical of some of his Manchester United team-mates was given as a reason for his departure after 12½ years.
Asked if he could envisage a time when he would have a good relationship with the Scot again, Keane told The Sun: "I wouldn't have thought so, no. He's a busy man and I'm fairly busy.
"I said before I was disappointed the way I was treated at the end, nobody will change that. But that doesn't mean to say I'm bitter and twisted towards Man United. Far from it.
"The worst thing is that when you have been associated with a club you still have loyalty towards it no matter what way I finished and no matter what my relationship with the manager might be.
"I can go back there, I just wouldn't be comfortable so that's my choice."
On their spat, Keane said: "I just thought the young players needed to buck up their ideas. The boy Phil Jones was speaking before the Basel game saying, 'I've nothing to prove', and my attitude was every time you walk out on a football pitch you've something to prove.
"I understood where Ferguson was coming from. It was only natural he was going to come out and have a dig back because he's going to defend his young player and he's going to be upset after a defeat.
"When there's snide comments coming in, I had a little dig back. That's the end of that now.
"But you have to defend yourself when people are being critical of my managerial record. I said at the time he should remember the players who helped him get the record he's got - Nicky Butt, those type of lads.
"I remember the lads who did well for me at Sunderland and Ipswich."