Roberto Mancini is ready to test the depth of his Manchester City squad as they begin their tough January schedule with two games in three days. The Premier League leaders travel to Sunderland on New Year\'s Day before hosting Liverpool on 3 January. City then face arch-rivals Manchester United in the FA Cup and have a two-legged League Cup semi-final with Liverpool, as well as games against Wigan Athletic and Tottenham Hotspur before the end of the month. Mancini said: \"It is impossible to play in two days with the same players, this is sure. January will be a key month. We will have important games - FA Cup, Carling Cup, four in the Premier League. I think this month will be very important.\" City saw their two-point advantage at the top of the Premier League wiped out as they were held to a goalless draw at West Bromwich Albion on Boxing Day. They now lead the table only on goal difference from Manchester United, and could even be second by the time they kick off at the Stadium of Light as Sir Alex Ferguson\'s men return to action tomorrow. Mancini anticipates a tight battle with the neighbours throughout the winter and spring, and believes the final reckoning could all come down to their derby clash in four months\' time. United travel to the Etihad Stadium for their third-last game on 28 April. Mancini said: \"If we are strong enough, I think it will be decided with the game at home, probably.\" Injury updates Mancini expects right-back Micah Richards to be fit for Sunderland after being rested at West Brom due to a calf problem. Left-back Aleksandar Kolarov is also coming back into contention after six games out with a groin injury. \"We didn\'t want to take any risk with Micah because we play a lot of games in the first ten days of January,\" the Italian manager explained. \"It is better. Kolarov is okay - it is the same situation.\"