Scholes was carried off after 16 minutes of Tuesday’s Champions League match away to Aalborg following a tackle by Thomas Augustinussen.
The 33-year-old is expected to sit out up to 15 matches and he could struggle to play again in 2008.
It is a major blow for United’s already depleted midfield. Michael Carrick faces another month on the sidelines with a broken foot, while Owen Hargreaves has struggled to shake off knee tendinitis.
Darren Fletcher is expected to stand in as a holding midfielder, while the versatile John O’Shea is another option.
United are waiting for further injury news on striker Wayne Rooney, who scored the opening goal in the 3-0 win.
Rooney came off with an ankle complaint after an hour and could miss England’s forthcoming World Cup qualifiers against Belarus and Kazakhstan.
Manager Sir Alex Ferguson said he is unlikely to feature against Blackburn Rovers on Saturday, and he has 10 days to recover before the Kazakhs visit Wembley for a Group 6 qualifier.
“Wayne felt his ankle. We hope it is not ligament trouble - but he is doubtful for Saturday, I would imagine,” said Ferguson.
Young Brazilian right-back Rafael Da Silva also came off injured, although his absence will not be missed as Gary Neville and Wes Brown are available to face Blackburn.
Reda Maher + Alex Chick / Eurosport
