Milan are interested in midfielder Axel Witsel and D'Onofrio confirmed a visit from their director Ariedo Braida last week.
D'Onofrio said: "Milan? On Friday I saw the match with Braida but he told me nothing about Witsel. He was there to see several players including surely even Axel.
"What is his value? I do not know, it depends. We have sold Fellaini for €20 million, Witsel is a player of that level. Let's say for 12, 15, 18, 20 million.
"Will he be again next season at Standard Liege? He has many offers, it will not be easy to hold him at Liege."