The Red Devils are one of a trio of Premier League teams – the others being Chelsea and Liverpool – thought to be interested in the Serbian international, who is being hailed as one of Europe’s top talents.
Matic swapped Stamford Bridge for Lisbon in 2011 as part of the deal that took David Luiz to London, and has flourished since being given regular first-team action.
His excellent performances have alerted United, with David Moyes keen to bolster his midfield options in January.
Matic is believed to have a £40m release clause in his current contract, which the Scot may be forced to trigger with Benfica in no hurry to sell.
The player himself is thought to be open to a transfer back to England in a bid to prove himself after being cut loose by Chelsea.
United are also thought to have been watching Nicolas Gaitan and Ezequiel Garay.
The winger and centre-back are believed to be two other names of Moyes’ wishlist ahead of the New Year.
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