The youngster joined Roma last summer for €13.4m from Basaksehir.
“He was about to sign for Manchester City, my son called and told me everything was ready," explained agent Omer Ozun on Mediaset Premium.
“I wasn't happy with it, so I called the Basaksehir President and told him to start negotiations with Roma. He replied that he'd do it for me.
“Under is really mature, he has the right mentality to be a star and is fortunate to be working with an intelligent Coach like Eusebio Di Francesco and director of sport like Monchi.
“These factors will make him a great and he is the pride of Turkey."
Under's form has attracted interest from various European giants.
“I cannot deny that he is tracked by all the big clubs, as everyone was surprised by his performances. My advice is for him to stay at Roma for at least another two years, as he needs to grow.
“Monchi received a lot of offers after the victory over Barcelona, but he's not interested."