Pep Guardiola is uncertain just how long Benjamin Mendy will be sidelined after picking up a knee injury last weekend.
The 23-year-old, who joined Manchester City for £52m on a five-year contract in July, was replaced by Danilo after just 29 minutes of the 5-0 defeat of Crystal Palace.
He injured himself after going in recklessly for a challenge on Andros Townsend.
Now the French international is expected to be sidelined for a significant period of time, although City will know more after Mendy visits a knee specialist in Barcelona.
Speaking after the 2-0 Champions League win over Shakhtar Donetsk on Tuesday, Guardiola said: "I think it is going to be a major setback.
"We are going to see finally what he has."
He added: "I don't know (how long he will be out).
"Wait until Thursday but I am pretty sure that it will unfortunately be a little bit longer than we expected or would like."
And whether or not to consider a replacement for the left back position in the January transfer window, the City boss said: "We thought next summer about looking for another left-back, another replacement, but we will see what we do.
"We have alternatives in our squad – Danilo, Fabian Delph, Fernandinho, can play there so we will see as we go along."