Mourinho signed Bailly as United manager, taking the Ivorian from Villarreal in his first season in charge at Old Trafford.
Bailly recalled to Mundo Deportivo: "I still talk to Mourinho. Sometimes he has called me when I have been injured, I consider him a good friend. Not everyone remembers you when you change clubs, and he has always been there in difficult moments. He tells me that the club believes in my abilities and that I have to die on the pitch.
"In the summer of 2016 there were many rumours. I was in the Ivory Coast, in the dining room at home with my mother when the phone rang. It was a Portuguese number: Mourinho. He told me to go with him, that he liked me since he saw me with Espanyol and Villarreal. And he explained to me that I was going to be important at Old Trafford. (Manchester) City were also interested, but if Mourinho calls you, you can't say no.
"You can't say no to Barça either. It simply did not happen because the interest was not public or as explicit as that of other clubs."
Asked about Mourinho's sacking, Bailly added: "I can't get too into that question, but I tend to look at the good stuff. And the titles that I have won with United were with Mourinho on the bench."