Pep Guardiola believes Manchester City will be without Raheem Sterling for "weeks" and he cannot be sure the forward will be fit for the Champions League trip to face Real Madrid.
England international Sterling suffered a hamstring injury in the Premier League defeat at Tottenham on Sunday and will miss this weekend's home match against West Ham.
City has not specified the severity of the damage Sterling has sustained, and Guardiola did not offer any guarantee that the 25-year-old will be ready to return to action before the end of February.
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After the West Ham game, City has a short in-season break, with its next match coming against Leicester City on February 22, followed four days later by a clash with 13-time European champions Madrid at the Santiago Bernabeu.
To lose a potential match-winner such as Sterling would be a major blow to City's hopes of beating the LaLiga leader.
Asked about Sterling's situation, Guardiola told a news conference: "Of course it takes weeks, but we will see before Leicester, Madrid and the rest of the games. I don't know right now.
"It is a problem. [Injuries are] always a problem, but it is what it is."
Guardiola said such injury absences are unfortunate - "especially for the players".
The Sane Issue
Leroy Sane needs time to develop confidence in his right knee before returning to match action for City after a six-month lay-off, Guardiola has said.
The Germany winger suffered anterior cruciate ligament damage in the Community Shield clash against Liverpool in August, forcing him out of the game and ending talk of an imminent move to Bayern Munich.
Bayern reportedly remains keen on Sane, with the 24-year-old having impressed for Schalke, City and at international level over the last five years.
City is determined to be careful with a player who is a valuable asset, and although Sane may come into contention for first-team football in the coming weeks, Guardiola will not rush the process.
"When you have an injury, especially like this one for six months … you need to recover the tempo, the rhythm, the confidence in your body, in your knee, don't think about the injury.
"It needs time. It's not like an ankle, for example, or a muscular injury. The injury to the knee always needs time.
"He needs weeks, [what is] important is the surgery was perfect and he's recovering incredibly well, and he will come back hopefully stronger than before, but right now he needs a little bit more time."