Villa resisted offers from West Ham and Chelsea for the Colombia striker.
Monchi said, "Unai is very sure of Jhon Durán. Very confident. He believes he can become one of the best strikers in the world in the next twelve months. He is 100 percent convinced.
"So, what's the problem? We also have Ollie Watkins and Durán wants to play. He thinks he's better than Watkins. It is normal because every player thinks he is better than his teammates. Managing Watkins and Durán is not easy but in the end it is the best thing for the team. Having two big strikers is better than just one.
Damian Vidagany, sporting director at Aston Villa, also said: "If you have Ollie Watkins, it is very difficult to find someone better because he is a fantastic striker, maybe among the two or three best in the Premier League.
"Ollie is extremely professional and a high-quality striker. So, did Durán want to leave the club? Yes. It's normal because he wants to play. There were no less than 40 clubs that wanted Durán - because they all wanted him."