I think Adidas have identified Sane's potential as the face of their brand. Unlike other German players, he's definitely got appeal to a younger, global market. He's already become a face worldwide thanks to the Premier League and City, so I'd guess they see him as a ready made commodity. Puma's arrival at City has probably concentrated minds and Bayern have been in bed with Adidas for a very long time. Some might say that Bayern's prolonged success has been based on their relationship with Adidas. They're almost the football team of the Adidas company.
Madrid?