The Argentine international has been linked with the Red Devils for some time, with rumours suggesting that a deal for the centre-back was virtually sealed over the summer.
However, David Moyes opted against drafting in the South American.
Yet, the Red Devils chief has remained keen on the 27-year-old, and was said to be considering a fresh end of season swoop.
But it looks as if Zenit will win the race, with Russian giants understood to have agreed a £35m double deal involving Garay and former Bolton attacker Rodrigo.
Benfica’s perilous financial position means that they are unable to keep their star players, and are willing to sell to the highest bidder.
Zenit are one of European football’s financial superpowers, with their backing from Gazprom allowing them to compete with the continent’s elite teams for the very best players – including Hulk who opted for a big money move to the club over a number of more prestigious outfits.