Christian Pulisic was unable to play against Brighton on Monday night as Chelsea face a longer wait for their star winger to return.
The US international suffered a hamstring injury in the FA Cup final defeat to Arsenal at the start of August.
And while Frank Lampard was optimistic Pulisic would be fit for the start of the 2020/21 season, he has not recovered in time.
The 21-year-old, who now wears the No.10 shirt at Stamford Bridge, returned to training last week at Cobham.
But the hamstring issue is still affecting him, and Lampard admitted Pulisic has taken a few steps back in his bid to get out on the pitch.
Asked why the American attacker was absent at the Amex Stadium, Lampard explained: “Christian was training with us last week.
Christian Pulisic did train at Cobham over the past week but he wasn’t match fit to play Brighton
“But he had a bit of discomfort a couple of days ago when he was trying to be in contention for today.
“It would have been a big ask for today and he has had to take a few steps back and we will have to see.”
Without Pulisic, Chelsea still saw off Graham Potter’s side on the south coast as Timo Werner and Kai Havertz made their debuts.
Christian Pulisic was taken off injured in the FA Cup final at the start of August
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