Here are 13 things you might not have known about the 24-year-old:
1. His full name is Faustino Marcos Alberto Rojo and he was born on March 20, 1990 (on the same day singer Gloria Estefan broke her collarbone in a bus accident and when Beats International's Dub Be Good to Me topped the UK music charts).
2. He can play as a left-sided centre-back or left-back, and has done so on numerous occasions for Sporting Lisbon ...
3. ... but judging by this 'Rabona' clearance at the World Cup he doesn't have much confidence in his right foot. Mark Lawrenson helpfully suggests "he would have looked an ass" if he'd messed it up. NB Rojo should ask Argentina teammate Ángel Di María how to perform a Rabona.
4. He can also be deployed further up the pitch as a winger, which might be why he is so attractive to Van Gaal who prefers wing-backs in a 3-5-2 formation. When within shooting range he is not afraid to have a crack, and has been known to score some wonder goals, including this one for Estudiantes de La Plata (his local side who he joined at the age of 10) ...
5. Rojo did have a good World Cup on the whole and played every one of the 120 minutes during the final defeat to Germany. Indeed, he was named in the team of the tournament having made 15 interceptions, won 17 tackles and completed 191 passes. In the semi-final against Van Gaal's Holland, he helped his side keep a clean sheet, and even nutmegged Arjen Robben.
6. He used to play in Russia (and wore gloves). He signed for Spartak Moscow from Estudiantes in December 2010 on a five-year deal, but only lasted the 2011-12 season after a torrid time, playing only 19 times. Rojo then moved to Lisbon for £3.5m in July 2012.
7. However, 2011 wasn't all that bad for Rojo: he made his international debut. It was a February friendly on home turf, and Argentina defeated Portugal 2-1 thanks to a last-minute Lionel Messi penalty. He has since accumulated 28 caps. And his only goal was a crucial one: the winner in Argentina's final World Cup group match against Nigeria:
8. Good news for United: Rojo can already speak English, according to his leg tattoos, which read 'Pride' and 'Glory'.
9. He has lots of other tattoos, too:
10. According to transfer rumours, he has attracted the likes of Barcelona, Real Madrid and ... Southampton, who were genuinely interested in him.
11. He is married to Eugenia Lusardo a model for a Lisbon-based lingerie firm called Dama de Copas. And the couple have a daughter called Morena (who they affectionally call 'More').
12. Rojo means 'red' in Spanish, so it would be highly ironic and mildly amusing were he to join the Red Devils (sorry).
13. Not everyone is convinced he is any good, including this Portuguese journalist:
