The Daily Telegraph report that Shaw may not play again in Red Devils colours this year.
Already without the services of Marcos Rojo, Phil Jones, Rafael andl Daley Blind, the latest injury news threatens to derail Manchester United's European qualification hopes.
The 19-year-old suffered ligament damage and was forced off the field after 15 minutes against Arsenal last Saturday.
Signed for a record £27 million from Southampton at the end of last season, Shaw will not play for at least a month and could miss the entire festive season programme.
Shaw out for at least a month
Cape Town - Manchester United were dealt a major blow as left back Luke Shaw was ruled out for at least a month.