Diego returned to the Bundesliga just one season after joining the Turin giants from Werder Bremen.

The player moved to the German club for 15.5 million euros last month, almost 10million less than what Juve paid for him last summer.

"Regarding Diego's transfer, it is the club that needs to give an explanation," said Del Neri to Gazzetta dello Sport.

"I can only say that he is a great player and I wish him the best of luck in Germany but with (new signing Fabio) Quagliarella we have more presence in the heart of the area.

"Our Diego is called (Alessandro) Del Piero. He is a very important player for Juventus.

"I am happy with the transfer market."

Italian pair Alberto Aquilani, on a season-long loan from Liverpool, and Quagliarella were among the acquisitions made by Juve this summer.