He remains largely unknown, having played for Penarol in the Uruguayan league. Many football fans had never even heard of him, so this summer's FIFA U-20 World Cup gave us the chance to catch a glimpse.
What are United fans in for with David Moyes' first signing? Let's take a look at what we've learnt from his performances in Turkey so far.
Varela is hardly the typical South American full-back, which can be taken as a positive if you're a Manchester United supporter.
Billed pre-tournament as a a flying full-back with a penchant for attacking, he's turned out to be far less raw and rash than both Rafael and Fabio were at a similar age.
While able to get forward and very much eager to do so, he doesn't neglect his defensive responsibilities and shows considerable consciousness for the defensive line.
Working well with central defensive leader Jose Gimenez, Varela picks his moments well and works in turn with right-sider Diego Rolan.
Uruguay excel in possession football and play out from the back. The defensive line drop into a group of four before moving forward, ensuring the correct foundations are in place to protect against counterattacks.
Going forward he can cross on the run and possesses a monster long throw when given the chance. He's comfortable in possession and uses his angles on the touchline wisely, creating passing avenues.
Varela's defensive consciousness is good, but he's still got a lot to learn in being proactive to cut out danger.
That's understandable given his age and limited experience, and the Manchester United coaching staff will likely be able to work wonders with his game.
Dropping into line alongside your centre-half is fine, but he's slow coming out to meet his marker—particularly wingers who hug the line—and invites crosses and underlaps from runners.
Hesitancy is natural, especially at an international tournament, but he's far less all-action in his work than Uruguay's left-back Gianni Rodriguez.
It's early days for Varela and tournament football is a different arena, but he's only impressed in his outings so far.
He's a very different animal to first-choice incumbent Rafael, giving David Moyes good flexibility and variety in a position typically difficult to fill.
We won't see too much of him in his first season in red, as he'll primarily be learning from the professionals on how to get up to Premier League speed. But he has the natural physicality and nous to succeed.