Sane, 22, was left out of Germany's World Cup squad, but has returned for Thursday's Uefa Nations League tie with France and a Sunday friendly with Peru.

But he is yet to start for City this season, and was dropped on Saturday.

"Sometimes you have the feeling with Leroy's body language that it's all the same if we win or lose," Kroos said.

"He's a player who has everything you need to be a world class player but sometimes you have to tell him he has to perform better," the 28-year-old Real Madrid midfielder added.

Sane won the Professional Footballers' Association Young Player of the Year award for 2017-18 as he scored 10 goals and assisted 15 times in the Premier League last season.

But he has played just 30 minutes from the bench in City's new league campaign, and was left out of the squad altogether for Saturday's 2-1 home victory over Newcastle.

"What is crystal clear is his quality, his pace, his left foot. If he performs, he's a real weapon," Kroos added.

"He has the quality, especially for us, but maybe the head coach looked at his performances for the national team and wasn't happy.

"He was fantastic for City last year but Pep [Guardiola] has the same problem at the moment - he's trying to get the best out of him."