Borussia Dortmund manager Jurgen Klopp says he is heartbroken to see his former star player Shinji Kagawa playing only a peripheral role at Manchester United.
The 24-year-old Japanese midfielder left Dortmund for Old Trafford last year and, although he ended his first season in England as a league champion, he was often left on the bench or asked to play in an unfamiliar left-midfield position.
"Shinji Kagawa is one of the best players in the world and he now plays 20 minutes at Manchester United -- on the left wing!" Klopp told Tuesday's edition of British newspaper The Guardian.
"My heart breaks. 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."
Klopp, whose side tackle Bayern Munich in Saturday's Champions League final at Wembley, has already seen attacking midfielder Mario Goetze commit to join Bayern for next season, with striker Robert Lewandowski tipped to follow suit.
He says it will be impossible for Dortmund to challenge Bayern's stranglehold on German football if the club's best players do not stay put.
"One year before that (Kagawa's departure), Nuri Sahin went because Real Madrid is the biggest club in the world," he said.
"If players are patient enough, we can develop the team into one of the biggest in the world."
Dortmund's run to the final has seen Klopp linked with managerial roles at some of Europe's most high-profile clubs, but he says he has no desire to leave.
"In this moment, I don't think of anything else," he said.
"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."