United signed the 20-year-old Uruguayan from Penarol on a five-year-contract this summer but he could move straight back to South America to continue his development with Argentine giants Boca interested.
"It could be a good solution," Varela admitted in an interview with Tutto Mercato Web.
"I would be able to play continuously for a year but I'd be always thinking about returning to United who are a club that believed in me."
If he stays in Manchester, Varela will provide competition for first-choice right-back Rafael, who enjoyed his best season for the club last term.
When Varela completed his move to Old Trafford in June he said: "I'm very pleased to be a part of this club, one of the best teams in the world.
"As everyone in the world knows, this is a huge club that has won everything and I really hope that continues.
"I'm very lucky there are quite a few Spanish-speakers here. It will certainly help me settle in."