The 23-year-old defender has been a standout performer since his summer arrival, helping City to 17 clean sheets in his 26 appearances.
Guardiola has been pleased with how quickly Dias has adapted to life in England and credits his work ethic and attitude for his superb form.
“Absolutely, so far,” he said when asked if Dias is one of the best signings of his City career.
“He settled in immediately. He is a guy who lives 24 hours for his profession.
"Everything he does on and off the pitch - eating, sleeping, recovering - is to be perfect for the 95 minutes of the game.
“It depends on him to maintain it. Hopefully we can help him to grow.”
Dias has featured in all but three games since making the switch from Benfica and his partnership with John Stones has earned plenty of praise.
A mean defence has been central to our rise to the top of the Premier League table and, with City conceding just twice in our last 12 league games, Guardiola admitted that Dias' performances have made him a certainty for selection.
“Right now, yes,” he said after being asked whether it was difficult to consider leaving his summer signing out.
“He's not just a player who plays good, he is a player who makes the other guys play good too.
“He is talking for 90 minutes, communication, 90 minutes believing, 90 minutes saying what we have to do in every single action.
“When that happens, it is difficult for me to drop him.”