Even though Sir Alex Ferguson has not confirmed when he will step down as United manager, reports continue to build which suggests the hunt for the Scot's successor is underway.
But club legend Sir Bobby has admitted that he wouldn't like to see the former Chelsea boss manage the side, despite his positive coaching quality, because of aspects of the Portuguese's behaviour.
"A United manager wouldn't do that," Charlton wrote in The Guardian, referring to the notorious incident when Mourinho poked Barcelona coach Tito Vilanova in the eye during a heated Clasico clash.
"Mourinho is a really good coach but that's as far as I would go really. He's the manager of Real Madrid and we expect to play them in the Champions League by the end of the season."
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That view is certainly backed by his record. Since 2002, Mourinho has not gone 12 months without winning a trophy, claiming seven League titles, ten domestic cups and three European trophies in 10 years in charge of high-pressure clubs such as Porto, Chelsea, Inter and Real Madrid.