United's lack of appreciation of the midfielder was demonstrated when they agreed to take a huge loss and sell him back to Dortmund for a mere £6.4m.
But teammate Subotic told the London Evening Standard: "Shinji is hungry to prove his worth and play regularly again. In training he's been great and determined and showed it against Freiburg. We all know he wants to do it.
"When he left for English football two years ago I wished him all the best and didn't question whether he was going to make it there or not.
"He has a lot of quality and I don't know why he didn't make the breakthrough at Manchester United. It could be put down to a number of factors. The coach changed a few times and that can be tough, I have experienced that with the national team.
"The most important thing is that he's at our club now and when somebody feels good, he will play better and Shinji has already shown that with a wonderful display against Freiburg."
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