He will have been impressed as Garay helped his side keep a clean sheet, in a 1-0 win away to bottom club Beira-Mar.
It was the second of two scouting missions in as many weeks for Ferguson, who was at the Porto game to watch Eliaquim Mangala last week.
The reports certainly indicate United are stepping up their search for a centre-back at the end of the season, with question marks over the long-term futures of Ferdinand and Vidic.
However Garay would cost more than £15 million, with some reports claiming he could cost over £20 million.
Are United ready to splash out that much on a centre-back?
It will depend on how accurate reports are regarding Cristiano Ronaldo's return, but Sir Alex Ferguson was critical of these at the weekend, describing them as 'false hope'.
26-year-old Garay has 11 international caps for Argentina and has previously played for Real Madrid, featuring eight times under Jose Mourinho in 2010/11.
If he gets a chance, if he is serious about the defender, could Sir Alex have a quick word with his opponent tomorrow night?
Watch him scoring for Madrid below...
image: © jansolo09