Derby player-coach Wayne Rooney feels Manchester United were wrong to sack Louis van Gaal.

Rooney is convinced that United's decision to axe Van Gaal less than 24 hours after winning the FA Cup in May 2016 was a ­massive blunder.

Rooney said: “I was devastated when Louis was sacked.

“For me, it was an absolute joy to work with him.

“We should have kept him for a third season. We would have been so much stronger.

“I felt things were improving and players started to understand his vision. In those two years I learned more than under any other

manager.

“This is why I will be forever grateful to him. Not just for making me captain, but also for all the trust and belief he had in me.

“We didn't have the best team in the league anyway, but we could not afford to have 12 players injured.

“Our best XI was good enough to play in the top four, but once we got injuries we got in trouble ­because we did not have the same quality in the squad as in the years before."