Sane was left off the final 23 man squad for Germany's World Cup campaign - which ended after the group stages.
But his club manager believes the rejection will only spur him on to take his game to another level.
"I think it's the past," said the City boss during his press conference on the club's pre-season tour of the United States.
"Jogi Lowe, the national trainer, decided what's the best for the national team.
"Leroy, has to accept that this decision may make him stronger. He's so young and in two years it is another European Championships and then in four years another World Cup.
"He has to improve his game, try to keep the levels he showed last season. We are so happy to have him here."