The Red Devils were heavily linked with the Argentine over the summer, but were unable to push through a deal during a frustrating few months for David Moyes.
However, the Scot is now ready to revive his interest in two weeks’ time after witnessing his side make a below par start to the season.
Although his midfield options are believed to be the greatest concern, Moyes is also keen to add a fresh centre-back to his squad with doubts surrounding the fitness and longevity of Rio Ferdinand and Nemanja Vidic.
Garay is thought of as the ideal player to step into the heart of the club’s defence, however United may struggle to convince Benfica to sell in the New Year.
But, the enforcer – who his enjoying an excellent season on a personal note – may be tempted by a big move in the build-up to the World Cup, where he is hopeful of representing his home nation.
United have also been linked with Porto’s Eliaquim Mangala, but the Frenchman is said to be valued at upwards of £30m.