Pep Guardiola's side head into the derby unbeaten in the Premier League having won 14 of their first 15 games, but Mata insists they will struggle to maintain that form over 38 games.

And he has told City that United are ready to take advantage of any slip-ups -- starting with Sunday's clash at Old Trafford.

He said: "It's very difficult to win every single game and we need to be ready if they drop points.

"Physically, December is a very tough month. We play at Christmastime every two or three days and we need to be ready for that.

"If we can get out of the Christmastime with all the points then we could be happy because it means we will be in a better position than we are now.

"We play against Manchester City at Old Trafford and it's one of those games that everyone wants to play. One of those really special games that the Premier League has.

"Hopefully, first of all, it's a great game of football and, secondly, we can win."

If United are to become the first team to beat City this season, they will have to do it without Paul Pogba.

Jose Mourinho is confident Nemanja Matic will be able to return from a muscle injury while Marouane Fellaini has "a chance" of being fit, according to the United boss.

Fellaini or Ander Herrera are most likely to replace Pogba in the team.

While Mata accepts the France international is a "big miss" for such a key game, he is convinced the squad is good enough to cope.

He added: "He's a fantastic player. He's a very complete midfielder, he can do all things.

"He will be a big miss but another player will play and try his best. I think we have a good squad and have good players to replace any other player. Hopefully we can win for him."

City's impressive form this season has prompted former players Danny Mills and Shaun Goater suggest the title race may already be over.

Mata, though, insists they are wrong.

"They know how football can change," said the midfielder, who scored the winner when United beat City 1-0 in the League Cup at Old Trafford last season.

"I don't think they do [believe the title race is over] and if they do I don't think they really believe it.

"I remember a few seasons ago when United were ahead of City and then they won by goals [difference]. It's a crazy league and it's too early to think that it's finished. From City they will tell you the same."

A United win this weekend would cut City's lead at the top of the table to five points, but Mata says the race for the Premier League has yet to really get going.

He said: "We have just started December and December is a crucial month with a lot of games. If we arrive in a position where we want to be in February or March then we can think about whether we won on Saturday and they won on Sunday.

"We think about the bigger picture and for us we have to keep up the pace and keep winning and winning. It's difficult for everyone to win every single game so we are waiting for that.

"We are doing what we have to do. We would love to be first in the table right now but I think we are doing lots of good things.

"Now, especially on Sunday and during Christmastime, which we all know how difficult it is to win every single game, we need to keep that pace if we want to be in a position to challenge for the title at the end of the season. Hopefully we can do it."