The 30-year-old's Old Trafford career hit its latest roadblock as he was forced off early in the second half of Saturday's 3-2 Premier League win against Southampton.
Chile physio Pedro Onate said forward Sanchez would be "unavailable to play for between six and eight weeks".
"It was a bad knee injury so if it's four weeks or six, hopefully he'll recover quickly," the Norwegian told a press conference. PA.
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