The 26-year-old has been heavily linked with a move to the Premier League, with new manager David Moyes ready to make the Argentina international his first signing since succeeding Sir Alex Ferguson at Old Trafford.
Garay joined Benfica from Real Madrid in 2011, with part of that deal seeing the Spanish club retain 50 per cent of any sell-on-fee, which is why the Primeira Liga runners-up are keen to draw as much money as possible from the centre-back's probable sale this summer.
The South American stopper is understood to have a €20million release clause written into his current contract at Estadio da Luz, and Manchester United are about to trigger negotiations with their long-term target.
United have also been linked with a move for Garay's team-mate Nemanja Matic, but that was Ferguson as opposed to Moyes credited with an interest in the former Chelsea star's services.
Garay made 41 appearances in all competitions in 2012/13, but his efforts for Jorge Jesus's side were to no avail, after Benfica finished second to Portuguese champions Porto, and also lost the Europa League final against Manchester United's Premier League rivals Chelsea.