He got injured on the 14th Dec and City originally advised it would be a 4 to 8 week job. More recently Pellegrini has talked about some time in January.
As he's not yet back in full training, I've just listed below possible comeback dates as you'd think he'd need a week in full training at least before he's ready for a place in the squad.
Saturday 18th Jan, Cardiff City Home is 5 weeks away, then
Tuesday 21st Jan, WHU League Cup semi Away
Sat 25th Jan is the 4th Round of the FA Cup
Wed 29th Jan Spurs away