The forward started England's friendly with Scotland on Wednesday but had to make do with a place on the bench for United's opener against Swansea City on Saturday.
Rooney appeared as a second-half substitute at the Liberty Stadium and set up a goal as his side ran out 4-1 winners but feels that he still has further to go to hit his peak.
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"I might be lacking that bit of sharpness but hopefully that will come. I need to try and get a few more games in."
The forward, who has been the subject of two failed bids from the Blues during the transfer window, lamented the disruption of his summer through injuries.
"You always look forward to having a good pre-season," he added. "It's important you do that. Unfortunately I got the injury to my hamstring and then to my shoulder. It's been disappointing but you've got to deal with it."
Rooney also revealed his gratitude to England manager Roy Hodgson after playing 67 minutes in the 3-2 friendly victory against Scotland.
"I have been working hard on the training ground trying to get myself fit and I was just thankful to get the minutes in against Scotland. That's thanks to the manager," he enthused. "I had a few painkillers for the shoulder injury. It was great to have the minutes and now I'm looking forward to hopefully getting a few games."