The Red Devils slumped to their worst finish of the Premier League era under David Moyes last season but the Argentine expects that to be merely a temporary blip.
Sergio Aguero believes Manchester United will re-emerge as a genuine contender for the Premier League title this season under new boss Louis van Gaal.
United endured its worst Premier League campaign under David Moyes last season while bitter rival Manchester City held off Liverpool and Chelsea to claim its second triumph in the last three seasons.
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"This year I think Manchester United will be up there challenging us," he said at the club's CityLive event Thursday. "Then you have teams like Chelsea and Arsenal who, as always, will be there or thereabouts battling with us for the league.
"But the team I think who is most worthy of having the best chance to threaten is United, because they are not involved in any other competitions other than the English knockout cups and the league.
"That means they'll get more rest between games than ourselves and some of the other teams and that will work in their favor, like it did last season with Liverpool."
Aguero also revealed he is still several weeks away from making his City return after an extended World Cup campaign with Argentina that was hampered by injury problems.
"I got back here last week and the aim to begin with is two weeks of just hard work to strengthen the legs and to get my fitness right," he added. "Right now I need that because it's been a good while since I did even a mini preseason of at least a fortnight. By the third week I'll be fully 100 percent and ready to go.
"I have to get in an hour and a half early and start off with strength exercises and then I work on stability in my hips and sides and then the rest is more straightforward, just to strengthen the pelvic area in order to prevent any further injuries by the groin area of the sort that I'd been having."