The 25-year-old suffered a knee ligament injury during Uruguay's World Cup group-stage match against Spain and had to be stretched off as he held his head in his hands.
After being assessed by Uruguay's medical team, Ugarte will now travel to Manchester to undergo further tests which will likely reveal that he will be out until at least December.
Speaking on the injury, Ugarte said he will only come back stronger as he starts the road to recovery.
"A few days have passed since everything happened," Ugarte wrote on Instagram. "Suffering the most serious injury a footballer can face in one of the most important matches in my country's history, and seeing it end this way without being able to stay on the pitch and support my teammates until the final whistle, is something that will stay with me for the rest of my life.
"Hitting rock bottom will make me stronger in every sense, and I truly believe that's the case here. Without a doubt, when life wants you to stop, it finds a way to let you know.
"It's up to me to take the positives from this. Success in life is about starting again every time you fall. I'm incredibly grateful to the Uruguayan federation and United for being there for me from the moment it happened.
"A huge thank you as well to my family, my friends and everyone who has sent me messages of support during this time. I’ll be back stronger."
Ugarte's future at Old Trafford remains uncertain as he is consistently highlighted as one of the players who the club are seeking to sell.
His injury now makes that awkward, and he may now have to stay at the club until the January transfer window at the very least.
Ugarte failed to score or assist across all competition last season as he struggled to impress in 22 appearances under both Ruben Amorim and Michael Carrick under which he was never a favourite.