Ahead of Sunday's Premier League clash between the teams, the former Portugal manager was quoted in British newspapers saying he has a father-son relationship with Ronaldo.
"When I was with Portugal, I had to choose three players every year for the World Player of the Year award," he was quoted as saying in Saturday's Daily Mail.
"Now these three players are with me, it's good for me - maybe next season Cristiano is with me. Tell him, if he wants to change I'll open the door for him."
Scolari comes up against the 23-year-old winger for the first time since the Brazilian quit as coach of Portugal where he helped Ronaldo develop his skills in the national team.
Scolari, who left after Euro 2008 to join Chelsea, added: "When I arrived in Portugal, Ronaldo was a kid, a young boy of just 17. At that time he had a good character, but he was already thinking about his future.
"He has improved a lot since, more so in Manchester than with the national team. He spends 11 months of the year with United and only one with the national team, but I have watched him improve.
"He will leave United one day... If he goes to another club, whether in one year or two years, I don't know. He's my friend. I like him as a father likes his son. But his life is his life.
"Next season I can see him as captain of Portugal because people like him and he has the confidence. He's a good man, he has grown up and is more mature."
"Now he is one of the three best players in the world."