Borussia Dortmund chief Sebastian Kehl has offered his explanation for Alexander Isak struggles with the Germans.

Newcastle and Isak host Dortmund in the Champions League tonight.

Isak has scored seven goals in eleven competitive matches this season and is celebrated in England. Kehl believes that the striker joined Dortmund too early.

"Alex has always had enormous potential, you could see that when he was with us. But maybe it wasn't the right opportunity in terms of timing to be able to give him enough playing time and develop him further," he told Ruhr Nachrichten.

"Alex took a small step back and then a big step forward. He has developed really well and is a good guy with a lot of quality. He is in good shape and will be looking forward to the reunion. Of course we hope he doesn't score against us."