Kagawa and Powell are set to make their debut during their tour of South Africa and China.
"He's trained with the lads and looks really sharp. I've seen him play a couple of times for Dortmund, and in the German Cup Final as well, and he's always impressed me.
"He's got a fair understanding of the English language, which will make his life easier. He probably already speaks more English than Anderson, so he's doing well!
"Nick Powell scored a ridiculous goal in the play-off finals, so he looks a really good player as well."