Bayer Leverkusen have told Chelsea they have to complete a deal for Kai Havertz by August 28.
Havertz is keen to join the Blues, but both clubs have failed to agree a fee.
Bayer are demanding for 90million, while Chelsea are willing to pay 70million.
Leverkusen’s players will report for preseason next Friday and want Havertz future to be sorted out by then.
The Bundesliga side saw their season ended after a 2-1 defeat to Inter Milan in the Europa League quarter-final and are now set for fresh talks with Havertz.
The club’s CEO Fernando Carro said last week: “It was always clear that we will have talks once the Europa League season concluded.
“Kai has voiced his desire to make the next step. At the moment, I can’t say whether this will work out in the near future or not.”