Petit, who won the Premier League with the Gunners in 1998, told the Daily Star: "I think Manchester United have dropped too many points. They are missing a balance in their team.
"I am still questioning why they are playing Wayne Rooney in midfield - and why they are still playing with two holding midfielders.
"Manchester United have enough power to impose their strengths on opponents.
"David Moyes is a very good manager but there will be more and more pressure on him. He needs wins and the next two league games are massively important. After those they have Arsenal at home.
He added: "As manager, you have to question yourself and find the right answers."
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