The 22-year-old has had to deal with plenty of criticism since joining the Citizens from Everton last summer in a mammoth deal worth around £50m.
Stones has featured 26 times in the Premier League for City, keeping just four clean sheets in that time, but Campbell has backed boss Pep Guardiola to get the most out of the England youngster.
"He's a wonderful player and I think he's got one of the best managers in the world to teach him and guide him through the pitfalls of football," he told Omnisport.
"He's lucky that he's there and definitely he's benefiting from having better players around him. I think his decision-making will get better in time.
"Playing in tournaments will allow him to get better. I think his future is bright and long may he continue learning. He's got the environment, the manager and the players around him to hopefully make him into one of the best defenders in the world in time."
Stones's overall defensive record makes better reading, playing a part in 25 clean sheets in 103 appearances for Everton and City combined.