Ziyech, who was signed in a £37 million deal from Ajax, was forced off in the second half of Chelsea’s pre-season friendly against Brighton on August 29.
The midfielder has suffered a knee injury and according to The Athletic, he will not be risked against Brighton on Monday evening.
The report also claims that Frank Lampard will be unable to call upon his new £50 million left-back Chilwell.
The England international suffered a heel injury in Leicester City’s win against Crystal Palace on July 4 and is still recovering.
However, Chelsea will be boosted by the prospect of having Christian Pulisic available for their opening Premier League fixture.
The Athletic reports that the United States international is due to return to training on Wednesday having recovered from the hamstring injury he suffered in Chelsea’s defeat to Arsenal in the FA Cup final.
Chelsea’s latest signing Kai Havertz is also in line to make his debut after completing his move to Stamford Bridge last week.
Havertz has yet to be given a squad number but the midfielder has asked for the No.29 shirt which is currently occupied by Fikayo Tomori.