In only his first season in England, the Portuguese defender was named as the Football Writers’ Association(FWA) Footballer of the Year earlier this week.
The 24-year-old arrived from Benfica at the start of the season for £62m and has played a key role in Pep Guardiola’s side taking back the Premier League crown from Liverpool.
Dias has featured 48 times across all competitions for Manchester City, who have also won the Carabao Cup and will contest the final of the UEFA Champions League against Chelsea in Portugal next week.
"It was unexpected, honestly. We knew about his quality but you never know how it is going to happen [after you sign a player]," Guardiola said ahead of Manchester City’s final league game against Everton on Sunday.
"Especially how he is happy helping the guys. The defender who plays only for himself is a problem.
"Ruben is always thinking about his partnership, the central defender, the holding midfielder, even the wingers.
"He is a guy who is so generous. He is a professional thinking about football 24 hours. He is so young.
"I'm pretty sure, in a short time, his mates and the backroom staff will choose him as one of the captains because he has shown he can lead.
"In the bad moments, always he is ready to help. He wants to improve, he listens. He admits his bad moments and the good moments he shares with his mates."