Borussia Dortmund manager Jurgen Klopp is unhappy with the way Shinji Kagawa has been used by Manchester United ever since the Japanese made a move to Old Trafford in the summer transfer window last year.
Kagawa was in world-beating form for Dortmund in the 2011-12 season, leading them to the Bundesliga and German Cups.
Seeing the obvious talent, Sir Alex Ferguson made a swoop for the 24-year-old playmaker last summer, but Kagawa has not quite shown the same form that he consistently showed at Dortmund.
With Ferguson having Robin Van Persie and Wayne Rooney in his lineup, Kagawa has been more often than not deployed on the left wing.
Sir Alex Ferguson has repeatedly said Kagawa will only get better and better with each season, and the Japanese did show signs of improvement during the final couple of months of the season.
If Rooney does leave the club in the summer, then the No.10 position will open up for Kagawa to exploit and David Moyes should be able to bring out the best in the talented playmaker.
Klopp, who has seen several big stars leave Dortmund for "bigger" clubs, believes Kagawa has been underutilized by United.
"Shinji Kagawa is one of the best players in the world and he now plays 20 minutes at Manchester United -- on the left wing! My heart breaks," he told the Guardian.
"Really, I have tears in my eyes. Central midfield is Shinji's best role. He's an offensive midfielder with one of the best noses for goal I ever saw.
"But for most Japanese people it means more to play for Man United than Dortmund. We cried for 20 minutes, in each others' arms, when he left.
"One year before that Nuri Sahin went because Real Madrid is the biggest club in the world. If players are patient enough we can develop the team into one of the biggest in the world."
Sahin has since returned to Dortmund, after agreeing a one-and-a-half year loan deal, but the likes of Mario Gotze will leave the club at the end of the season, with prolific striker Robert Lewandowski also tipped for a move away, with United, incidentally one of the prime candidates for the Polish international's signature.
Klopp's brilliance at Dortmund has also led to several big clubs tracking his progress, but the enigmatic German said he has no plans on leaving the German club anytime soon.
"In this moment I don't think of anything else," he added. "If I went to many clubs now and said: 'Hello -- bring me offers,' maybe some would start running. But I'm not interested because, for me, this is the most interesting football project in the world.
"In three or four years, if someone wants me, we can speak. But, for now, this is the best place for me."
Meanwhile, Rio Ferdinand is reportedly close to agreeing a new contract with Manchester United to extend his stay at Old Trafford.
Ferdinand, whose contract expired at the end of the season, is expected to sign a new one-year deal and the player's representatives confirmed an agreement was close.
"Talks regarding Rio's new contract are moving along nicely and hopefully we will have some news soon," Ferdinand's representatives told Sky Sports.
