The Premier League duo have been linked with the French youngster for some time, but were fearful of a huge offer from the Ligue 1 giants.
Monaco have emerged as big players in the transfer market after securing promotion back to the top tier, with their Russian owner, Dmitry Rybolovlev, having already pumped in excess of £150m into their squad this year.
Mangala was thought to be their top January target, but now is appears that their interest has switched to Saint Etienne’s Kurt Zouma.
The 18-year-old centre-back – a target for Liverpool – is one of the hottest properties in French football, and Monaco are keen to move for his signature as soon as possible.
A January move will likely shelve plans of a swoop for Mangala, clearing the path for United and Chelsea.
Porto are believed to be holding out for a release clause-triggering £42m offer for the 22-year-old.
Mangala is thought to be open to a move to the Stade Louis II, but has concerns over a lack of atmosphere at the stadium, due to the club having only a small following.
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