Zlatan Ibrahimovic has revealed he is still motivated by his falling out with Pep Guardiola at Barcelona.
Guardiola brought Ibrahimovic to the Nou Camp in 2009 but the relationship between the pair broke down and he was loaned to AC Milan after only a season before making the move permanent.
The Swedish striker has been outspoken in his criticism of Guardiola since and, when Manchester United face the Spaniard's Manchester City side in the derby next month, Ibrahimovic will be especially fired up.
In an interview with Fabio Capello on Fox Sports Italia, he said: "I learned from Barcelona, both on and off the pitch. I learned that in football any situation can change in 24 hours.
"The problem wasn't with me, it was with him, and he never came to terms with it. I don't know what his problem was with me.
"It is something that drives me, gives me adrenaline and extra motivation. It is normal after what has happened. I'm using it as a positive, not negative."
Ibrahimovic's United will travel to the Etihad Stadium on April 27 in what could potentially be a decisive clash in the battle for the top four.
But former United boss Sir Alex Ferguson believes the club should prioritise winning the Europa League to secure a Champions League place.
United are favourites to win the one major European title they have never claimed and will take on Anderlecht in the quarter-finals.
Ferguson told ESPN: "The thing is, we've never won the Europa League. We've never won (the) UEFA Cup, what it used to be. And we've got a great draw. I'm not saying it's a certainty, but they've got a great chance.
"If you win a trophy, it's important. It doesn't matter that it's not the Champions League - it's still a European trophy. And if you win it, you get into the Champions League. The incentive is greater to do that.
"And your CV gets bigger. If we won the Europa League? Fantastic. Add it to the European Cup, the Cup Winners' Cup, the Champions League - it's bigger and bigger. We also want to be the most successful club in England."