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 have 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.
After the West Ham game, City have a short in-season break, with their 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 leaders.
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".