Ramos played the full 90 in their win against Las Palmas for his debut on the weekend.
Mendilibar was asked if he would start in the Champions League and said today: "He will debut if I put it on. He is a leader, of course, and everywhere in clubs and in the National Team. He was already a leader at 17 years old at Sevilla.
"You are born a leader and Sergio is going to die being that. He can help us on the pitch and on the bench too."
"Yes, I said what I said. We have a style of play and the players must do what we ask of them. Football is universal but some adapt before others. The players know what we ask and want from them."
He added: "I want to have a good competition: for the club, for the fans, for me. I would love to go to the playoffs. This is new for me. But I don't have to silence anyone."