The Germany international has been in sensational form over the past week, scoring a brace against West Bromwich Albion in the EFL Cup and then adding a fine opener in the league win over Crystal Palace.
Sane also contributed a couple of assists against the Eagles on what was just his second top-flight start of the season, but Guardiola says that he was initially unhappy with the 21-year-old's fitness when he returned to the club in the summer.
"He didn't arrive good, he didn't make a good pre-season, he didn't deserve to play," he told reporters. "Now I have five strikers who all deserve to play. Gabriel Jesus is amazing, Bernardo Silva always creates, there's also Raz (Raheem Sterling), Leroy and Sergio [Aguero].
"Some of them are going to rest. I need them sharp, especially in the second half of the season. But, of course, Leroy is so important for us. He's a guy who runs in behind in the right tempo, at the right moment as well as anyone else in the world.
"He is improving at the simple things, the simple balls, not losing the ball. Before he had to improve in that. Any goal is important and he is scoring a lot of goals, creating chances, giving assists. He is a young player, 21 years old, and he is so important for us."
Man City have now won three successive league games by five goals or more - the first English team to do so since Blackburn Rovers in 1958-59.