The Pole impressed on loan at Charlton last season and was snapped up by the Rams in the summer for £7million.
But Milan chiefs had initially made an effort to sign him before the UEFA Euro U21 Championship where he represented Poland in the summer.
“I was hoping to get an opportunity with Unai Emery," he told Sportowe Fakty.
“Instead, I didn't fit into his plans and so I had to leave.
“Before the European Under-21 Championship, I received an offer from Milan, but then everything changed and nothing more was done."
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