"I can remember Wolfsburg being champions and it was because of him," he said. "He was the top scorer in Germany and that is not easy.
"But he played with quite a few good players up front if you compare Wolfsburg then with the team now. It is a big difference.
"They had Grafite, for example, who was a very good player. They had [Zvjezdan] Misimovic, they played in a certain system - the golden triangle with Dzeko.
"I think it is only a matter of time. If you play Dzeko every week then you will see he is a quality player.
"But of course you have got [Carlos] Tevez, [Sergio] Aguero, [Mario] Balotelli so they've got world-class players."