Pep Guardiola has no doubt Arsenal could challenge his Manchester City side for the title.
The Premier League leaders host the Gunners on Sunday.
Arsenal finished outside the top four for the first time in 21 years last season and their start to the current campaign was indifferent.
But after losing just one of their last seven games to climb to fifth, the Londoners’ season is starting to show potential and Guardiola is wary of their threat.
He said: “We are in November. They won the FA Cup last season. The prestige of the club, the Emirates Stadium – of course they are a contender.
“It is nine points. The difference (between us) is nothing, believe me.
“People consider we are going to play like the last two months all season. When that has happens I can say, ‘OK we have a big chance to be champions’ but nobody can assure you that. We have to fight.”
Guardiola believes this weekend could have a key bearing on the title race.
He said: “We know United are playing against Chelsea, so it is another game to make more advances on one of them, or both of them. That is why we have to be focused on an important game for us.
“At the least maybe (we could) leave Arsenal 12 points behind. It is a massive game for us for many circumstances, starting from the way we want to play, to try to win the game.”