The German side are worried about the recurring injury situation of Baba Rahman
The 22-year-old defender spent the entire of lat season on loan at the Royal Blues outfit in the Bundesliga. He made 21 appearances for Schalke 04, before sustaining an anterior cruciate ligament tear.
The Bild had earlier said that Schalke had reached an agreement with both Chelsea and the player to extend his loan spell but they might think through it again due to his deteriorating physical conditions.
"Our team doctor met Abdul in London. His knee injury is more complex and [his recovery] might be prolonged," Schalke sporting executive Christian Heidel told Bild.
"We will wait another four weeks and then decide with Baba and his agent whether [another loan] makes sense."