The Japan international has struggled to hold down a regular place in the United starting XI since his move from Borussia Dortmund two years ago.
The 24-year-old had his moments last season, including a hat-trick against Norwich, but he is yet to find the net in nine Premier League appearances this term - playing the full 90 minutes just twice.
"I still haven't scored any goals this season so I've felt very irritated," said Kagawa.
"This is the first time in my career that I haven't been able to produce so it's disappointing.
"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.
"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."
@ManUtd99 Without doubt the best 45 minutes I have seen from Man U in the prem this season was the second half against Swansea at Old Trafford. Kagawa was in his natural position, Fletcher played fantastically well in a role that Carrick has pretended to do for years and Januzaj was tearing them up from the wing. So what did the genius Moyes do next game? Dropped Kagawa and Fletcher for recently declared fit duo of Young and Jones; and they got butchered! Kagawa was a key member in a Dortmund side that would absolutely batter Man U, a side that battered a Bayern team team that at the time was only a Javi Martinez away from dominating Europe.- onspsv