Rooney is convinced the Reds will be challenging for honours this term, with Mourinho working hard behind the scenes to find the winning formula.
"I think he's been brilliant since he's come in," said the captain to MUTV. "Training has changed a lot. The training has been really good and it's interesting to see how he prepares for games with tactics, how we approach games, and it's been really good.
"I'm sure obviously we will come back and definitely be challenging this season."