The trio impressed for United in victory over Hannover.
"I played with Kagawa and Tom Cleverley in there as well and the three of us linked up really well I thought, at times anyway. Tom was a big miss for us last season. Obviously now with the Olympics he's up to speed, he's got his fitness and he will be an important player for us this season," said Rooney.
"Kagawa's been great. He's a great signing for us and I'm looking forward to playing with him in the season. I feel good. A lot of hard work in training, obviously it's the games what count and it was nice to have the 90 minutes."