The French centre-back was heavily linked with Manchester City last month, but the Sky Blues failed to lure him to the Etihad Stadium after baulking at the Portuguese champions’ valuation of their man.
This has left the door ajar for United, with David Moyes desperate to overhaul his failing squad at the end of the season.
The Scot spent £37.1m on Juan Mata last month – a club record fee – but he is still believed to have a vast budget at his disposal to guide his side back to the very top of English football.
Securing defensive reinforcements is now seen as a priority, with the likes of Robin van Persie, Wayne Rooney and Mata regarded as more than capable of firing in the goals needed for success.
Porto are thought to be unwilling to drop their demands for Mangala once the new transfer window is open, but United are prepared to pay what it takes to snap up the robust centre-back.
City may launch a fresh raid, and the Porto ace’s decision may hinge on Champions League football.