Hertha Berlin are in the middle of an unlikely injury crisis, with five goalkeepers injured and under a month to go until the new Bundesliga season.
Muller scored only five goals last season, enduring a 999-minute league goal drought, and faces increased competition.
RB Leipzig are "lucky" they don't need to sell star midfielder Naby Keita, according to Liverpool manager Jurgen Klopp.
Borussia Dortmund have been fined and handed a suspended stadium ban because of fans' behaviour at the DFB-Pokal final.
Mexico striker Javier Hernandez has agreed to return to the Premier League with West Ham, the club confirmed on Thursday.
Franck Ribery says he was not "completely happy" with last season and has demanded more playing time at Bayern Munich in the 2017-18 campaign.