Former United captain Young has revealed he 'couldn't understand' United's decision to sell Lukaku.
"I said it at the time, I couldn't understand the decision [to sell Lukaku]," Young told Sky Sports.
"Whether it was made quickly or not, Romelu has proved a lot of people wrong.
"He's worked unbelievably hard. There was talk that he was overweight and couldn't do this or that. He's smashed record and made history in Italy, he's been unbelievable for the club.
"For me he was fantastic even in the Premier League, to go out there and face another challenge, I think it was the right choice for him. He deserves all the plaudits he is getting."