Christian Pulisic is expected to be unavailable for Chelsea's Carabao Cup fourth tie against Southampton on Tuesday night at Stamford Bridge.
The 23-year-old has been out of action since the start of September after coming off with an ankle injury on USMNT duty against Honduras.
He was set to be out for around 10 days but Pulisic has now spent well over a month on the sidelines.
Prior to Chelsea's 4-0 win over Malmo, Tuchel admitted he was 'very, very close' to returning after receiving a setback.
"Right now, we are very very close," said Tuchel earlier this month.
"He was so close to come to team training last week but had a setback with pain. Nothing serious but serious pain. From there on we go. He is very impatient, he does everything. We see him suffer in every meeting. He is really suffering, he wants to be on the pitch and help us. Unfortunately, the injury takes it's time."
He missed the 7-0 win over Norwich City on Saturday as Tuchel confirmed his absence. He was thought to be training on his own last week which suggests he will remain out and unavailable for selection against Southampton on Tuesday night in the Carabao Cup fourth round.
Tuchel will also be without Romelu Lukaku (ankle) and Timo Werner (hamstring) against Southampton, but will welcome back N'Golo Kante back into the side.
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