The two sides meet this Sunday with the North Londoners eight points clear of United at the top of the table after a blistering start to the campaign.
United’s form is also on the up, though, as a 0-0 draw with Real Sociedad on Tuesday night extended their unbeaten run in all competitions to eight games.
And Rooney believes Arsenal — who haven’t won a trophy for over eight years — still have to show they can last the distance of the 38-game season.
“We’ve beaten Arsenal many times in the past. They are in good form at the minute, they’re top of the league, so we know it is going to be a difficult game.
“But we have to go into the game confident that this is the game that will bring us back into the mix.
“We’ll have to wait and see where they are in March. We’ve seen before that they’ve been in the top two until February, March time and then dropped off so it’s down to them to try and stay there.
“They are doing brilliantly and are in a great position so it is down to us to match them.
“We know we are playing better and are stating to do well. There are only 10 games gone so there is no big worry at the minute.”
Rooney started the 0-0 stalemate in San Sebastian, but was replaced by Robin Van Persie with half an hour remaining to keep him fresh for Sunday’s clash at Old Trafford.
Van Persie went onto miss a penalty and saw another effort strike the post as United failed to secure the win that would have all but sealed their place in the last 16.
The English champions still lead Group A by a point from Bayer Leverkusen with two games remaining.
However, Rooney was frustrated not to have taken all three points having had by far the better of the chances in a cagey encounter.
“We’re disappointed not to get the three points. I thought we were the better team, but overall it is another clean sheet and decent result.
“I think coming away from home in the Champions League, they are always difficult games. We had good chances so we feel we should have won the game, but a draw away from home is ok.”
And Rooney is sure that Van Persie’s spot-kick failure won’t affect his confidence ahead of the meeting with his old side at the weekend.
“Most forwards in the world miss penalties, it is one of those things. That won’t affect him I’m sure.”