David Moyes' men were beaten 1-0 at home by Everton on Wednesday and sit ninth in the table after their fourth league defeat of the season.
The loss also leaves the champions 12 points off leaders Arsenal, who beat Hull City 2-0 to extend their winning run in the top flight to three matches.
Despite the distance between the sides, Wenger is not discounting United just yet.
"It's still early. It is a surprising defeat (to Everton) but it is still early," he explained.
"We have just to keep winning to have a chance, and not worry too much about the others."
Jack Wilshere, Olivier Giroud and Theo Walcott all started Wednesday's win on the bench, while Nicklas Bendtner took advantage of a rare start to score his first goal of the season.
Wenger explained the need to rotate his side ahead of a run of fixtures in quick succession.
"Now we play Everton on Sunday, there is little distance between Everton and (the UEFA Champions League game against Napoli)," he explained.
"We play Wednesday night in Naples and Saturday morning at Man City, so for us it is a very, very heavy schedule."
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