"I still haven't scored any goals this season so I've felt very irritated," Kagawa told Sky PerfecTV. "This is the first time in my career that I haven't been able to produce so it's disappointing."
Juan Mata's arrival at Old Trafford is likely to decrease Kagawa's chances of first-team football.
"I pressure myself to score in every game but some days it feels like I just can't win. I know I have to overcome that," he added.
"Actually, if I can't it really shows that I haven't grown as a player. So because of that I have to really focus on the second half of the season and overcome that mental block."
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