Kagawa has started the last two games for United - and won both.
"He is a fantastic talent," McIlroy told the Manchester Evening News
"But the problem I think David Moyes has got is 'where do I play him?.' Clearly, you don't become a bad player overnight but he is still trying to find his best position.
"Personally, I think he is best suited to playing in the hole behind the main striker.
"But how do you get in there with the way Wayne Rooney is playing? So, it is an awkward one."
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