Chelsea left-back Baba Rahman spent the just concluded league season on loan with German side Schalke.
Rahman delivered some impressive performances for his loan club during the first part of the season but missed the second part of the campaign after suffering a knee injury at the African Cup of Nations.
It is hoped Rahman will recover in time for the end of pre-season and Schalke general manager Christian Heidel says the German club will wait until July before deciding whether to sign Rahman.
“Our team doctor met with Baba in London,” Heidel told Bild.
“His knee injury is much more complex and lengthy than anticipated.
“We will wait until July and then decide with Baba and his agent whether it makes sense to open negotiations with Chelsea.”