The Manchester United playmaker arrived at Old Trafford in 2012 and has struggled to win a place in the starting XI, netting just six goals in his 40 appearances for the Red Devils
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It is in stark contrast to his form at Borussia Dortmund, where he was a key member of Jurgen Klopp's side and Kagawa believes he must rediscover that level of performance at Old Trafford.
He told reporters: "I've never had so much trouble not being able to score goals. Right now it's just trial and error.
"The season's still continuing, so I just have to find a way to recover my form. This is my big challenge."
Kagawa was one of many underwhelming performances in United's 2-1 home defeat to Swansea in the FA Cup third round, but could have the opportunity to make amends on Tuesday at Sunderland in the Capital One Cup semi-final first leg.