Roy Keane has warned Manchester City to write off Sir Alex Ferguson at their peril.
Keane said City were worthy champions but to expect Manchester United to bounce back even stronger - and that his old United boss Ferguson will still be around for years to come.
"Never write off United. Never doubt United," said Keane.
"United always bounce back. It's in the nature of the club. They will probably buy one or two players, which they probably would have done even if they had won the league, and it's exciting for the people of Manchester.
"Sunday was a hard one for them to take, but I think United fans will actually enjoy that challenge because the games are closer."
Ferguson may have turned 70 but Keane believes the challenge of taking on City will inspire his old manager to new achievements - and that he has seen off all other challengers in the past.
Keane added: "When you are a manager in sport at the top level, the challenges will drive you on to another level and United have always responded.
"Going back over donkey's years when Blackburn had a decent spell, Arsenal, look at them they haven't won anything for seven years now, Chelsea, they are coming back a little bit now. Liverpool, look where they are now. United will enjoy that challenge. And you can see that in his eyes.
"People have written him off a few years ago when Chelsea won the league a couple of years running, saying he was finished, but he is still going strong.
"He will want to go out on a winning note but just listening to him and watching him he will go on for a few years yet. If they win the league next year, or the Champions League, I think he will carry on."