"Maybe it was a little bit too early but you could see his pace and his physical strength but without any experience it's difficult to keep your place and play regularly for Arsenal.
"That's why he moved back to Germany and got games with Werder Bremen and, later, at the highest level with Bayern. He has been involved in a lot of goals in a lot of games.
"He needs match practice and if you have match practice regularly then you can grow as a player and as a person.
"Now, without Sane [who is injured] he is our best attacking player in Germany."