Bayer Leverkusen are demanding Kai Havertz see out their Europa League campaign before any move away.
The Mirror says Bayer are insisting that Havertz must stay with them for the remainder of their Europa League campaign as Chelsea attempt to push through the transfer.
Leverkusen host Steven Gerrard's Rangers in the second leg of their last-16 clash next Thursday, with the Germans sitting on a 3-1 aggregate lead from the first leg.
Should they see off Rangers, Havertz and Co will play their quarter-final the following Tuesday, against the winners of the last-16 tie between Sevilla and Roma.
The semi-finals will then take place on August 16 and 17 before the final on August 21.