Rooney scored his 200th goal for United when he claimed a brace in Tuesday's 4-2 Champions League win over Bayer Leverkusen, but questions over his happiness at Old Trafford remain.
However, the 27-year-old England international says he is focused on letting his football speak for itself following a summer of discontent.
"I've put my head down and worked hard and tried to do everything right," Rooney told The Mirror.
"I've tried to show the right attitude. I've always felt that's a really important thing to do. That's paying off for me on the pitch. I feel fit and ready to do well.
"I feel good. I've had some good training the last few weeks. It's been stop-start with the injuries, but I've just kept my head down and worked hard and now I've played and got some goals.
"I feel great. The training is a bit different under the new manager - I remember it from Everton, it's more intense. That's helping me.
"I feel good and am glad to be out playing."
Rooney also backed manager David Moyes to succeed with the Red Devils and hopes they will be able to form a strong working relationship.
"He's a great manager and thoroughly deserves this job because of what he did at Everton. It's good to work under him and hopefully be successful together," Rooney added.
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