The 22-year-old was surprisingly left out of the Germany squad for the 2018 World Cup despite being named the Young Player of the Year in the Premier League last season.
Sane managed 14 goals and 19 assists for the Citizens last term, but Guardiola wants more from the German.
"It depends on him," Guardiola told the club's official website. "He needs more minutes and he needs to regain his principles in terms of playing without the ball. He has the talent to do that and we are happy that he scored. Still, he is far away from his best."
City will continue their preparations for the new campaign with a clash against Bayern Munich on Saturday night.