Ole Gunnar Solskjaer, a former team-mate of Rooney's at Old Trafford, is off to a flying starts as caretaker manager, winning his first game in charge 5-1 at Cardiff.
"Something had to change, It was the right decision," DC United striker Rooney said on BT Sport of the decision to dismiss Mourinho.
He added: "I stay in touch with a lot of people at the club, speak to them quite a lot - certainly this week - and I think, to be a successful football club, you need everything to be right.
"You need the staff at the training ground to be right, the groundsman whoever that is, they need to feel happy and that rubs off, that rubs off on the players and I think that relationship between some of the staff and some of the players obviously wasn't great.
"But I think also bringing Ole in, bringing Mick Phelan in, that already has changed. I think the staff down at the training ground are smiling, they're happy and that rubs off on the players.
"I think it's a good move for the club, while it gives them a bit more time to make sure they get the right manager in place in the summer."