Karl-Heinz Rummenigge warned Leroy Sane must show more desire and says Bayern Munich will be prepared to "kick his butt" if needed to get the best out of their big-money signing.
Sane has endured a difficult start to his time at Bayern and hit a new low when he was hauled off after being introduced as a substitute to replace the injured Kingsley Coman in the first half of a dramatic 2-1 win at Bayer Leverkusen on Saturday.
The winger, signed on a five-year deal for an initial fee of €49 million (£44.