According to Daily Star, the Japan international has not hit the field for the defending Premier League champions since the club purchased Mata from Chelsea for 37.1 million pounds.
The lack of opportunities for Kagawa has reportedly made him irritated under the new boss David Moyes.
The report also added that Kagawa was unable to replicate the form he showed at Borussia Dortmund which made former United boss Sir Alex Ferguson fork out 24 million pounds for the midfielder in 2012.
Though Kagawa had intended to move back to Bundesliga to his former club Borussia Dortmund, United, on the other hand, want to recoup as much as they had invested in the Japanese player.
However, United is ready to sell Kagawa to the highest bidder if Dortmund does not agree on exchanging their midfielder Ilkay Gundogan, the report added. (ANI )