Roberto Mancini says Manchester City cannot afford to lose the derby against title rivals Manchester United on Sunday. The reigning Premier League champions trail league leaders United by three points heading into the crunch game at the Etihad Stadium. In this fixture last season, City came out on top 1-0 after a cagey affair to move into pole position for the title, but Mancini believes United are a better team this campaign. United manager Alex Ferguson added Robin van Persie and Shinji Kagawa to his squad in the close season and Mancini feels those additions, and United\'s early advantage, means they are favourites for the title. \"They (United) can lose, they have three points more. We have three points less and we can\'t lose. I think they are better than us in this moment, but a derby is a derby,\" said the City manager. \"In this moment, probably United (are favourites for the title), but the season is long. \"I agree because they were a strong team (last season) and they bought van Persie and Kagawa. They put another 25 goals into the squad. \"It is an important game. They have three points more than us and they have a small advantage, but a derby is a really difficult match for both teams. \"It is not the season (that will be decided), because we have seven months after.\" City thrashed United 6-1 at Old Trafford early in last season\'s campaign and saw off numerous teams in spectacular fashion on their way to their first league title in 44 years, but they have not been as ruthless so far this term. Mancini\'s side also crashed out of Europe on Tuesday after defeat against Borussia Dortmund saw them finish bottom of their Champions League group, which meant they failed to qualify for the Europa League as well. But the Italian believes it is \"normal\" for City as a young team to find it difficult to retain their Premier League crown and believes last season\'s win at Old Trafford was a key turning point for their season, hinting a win on Sunday could do the same. \"This is normal. This can happen, a young team like this,\" he said. \"This is normal after winning the championship after 44 years. \"You need to work harder. You need to work more. It is normal that it is more difficult in the second year. \"It was important for us because we played the first derby away and we won 6-1. There are some important games that can change your season and the derby (last season) was one of the first games like this for us.\" United beat City to the signing of £24 million ($38.4 million, 29.7 million euros) striker van Persie from Arsenal, capping a frustrating summer for Mancini, who missed out on a number of targets. Van Persie has scored 13 goals so far for United, but Mancini insists they are not worried about missing out on the Dutchman and will find the goals to lead them to the title. He said: \"In this moment, it is in the past. We have good players. We can improve this situation because we don\'t score a lot of goals, but I am sure if we continue to work, we can improve.\" The City manager also revealed he will give Gael Clichy (ankle), James Milner (hamstring) and David Silva (hamstring) until Sunday morning to prove their fitness, but Aleksandar Kolarov (ankle) is definitely out. \"We don\'t know for sure (about injuries),\" said Mancini. \"We decide this Sunday morning, but we try to recover Gael and James. We can\'t take a big risk because we have a lot of games from now to the end of December and we need to have all the players ready.\"