Ilic joins the Serie A outfit in a deal worth €7.5m. City retain a buy-back option in Ilic's deal.
He has penned a contract that runs to June 2026.
The 20 year-old spent last season on-loan with Hellas Verona. He already has two senior caps for Serbia and last season contributed three goals in 30 appearances for Hellas Verona between Serie A and the Coppa Italia.
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