Manchester City will be without midfielder James Milner for Saturday's Premier League game against Everton.
The 26-year-old limped off with a hamstring injury soon after scoring the second goal in City's 2-0 win at Wigan on Wednesday.
The England international could also be doubtful for next week's Champions League trip to Borussia Dortmund and the derby showdown with Manchester United which follows, but City are not yet sure of the seriousness of the problem.
Milner, who came on as a substitute at the DW Stadium, had been making only his second appearance since returning from a lay-off with a similar injury.
Mancini said: "James is out for Saturday. We will try to recover him for next Sunday but we don't know.
"He played against Chelsea and played very well. He came back after injury, now he played 20 minutes and had a hamstring injury.
"We are disappointed because James was in good form in this moment."