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.
He added: "As manager, you have to question yourself and find the right answers."
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