The Pole left Napoli for Inter in Bosman transfer this summer.
Zielinski told the Foot Truck: "At one point, Bruno Fernandes wanted me to sign for Manchester United. We are still in touch, we speak very regularly. We played together at Udinese and in one of those games we practically beat Milan alone."
The Pole also revealed he was close to joining West Ham in 2022.
He said: "(Napoli president Aurelio) De Laurentiis was already convinced of the offer of €35m. They were already looking for medical care for my wife and children and a place to live.
"Coach (Luciano) Spalletti called me once and asked me what I would do, and I replied that I would prefer to stay and fight for the title. He told me he wanted me to stay and that I would be Zielinski's best summer. I stayed because I didn't feel like I was in London either."