But the transfer window only closes in October. Ideally, everyone would want to get their transfer business done fast and early (GET MOVING MARINA, FFS!) but players moving clubs while the league has started and the transfer window is not closed is nothing new. We have seen such cases in the past.
If Leverkusen don't sell him this summer, then good luck to them because they risk keeping an unhappy player and potentially, getting less money next year.