Sanchez was replaced after 52 minutes of the 3-2 victory at Old Trafford after a challenge from Saints defender Jan Bednarek and United's own medical staff have yet to provide a prognosis.

But Onate said that exams of Sanchez's condition showed he had suffered distention of the medial ligament, which would take a number of weeks to heal.

Onate told El Mercurio: "There won't be any problems for him to be at the Copa [America], because he'll be out for between six and eight weeks.

"Alexis may even play again before that time. Plus, there's a long way to go until the Copa America.

"The distention of the medial ligament is an annoying injury, but it's not so complex."

United will be without Sanchez as they travel to Paris Saint-Germain for the second leg of their Champions League last-16 tie on Thursday (AEDT), where it hopes to overturn a 2-0 deficit.

Sanchez has made just eight Premier League starts for the club in 2018-2019, scoring once.