Rooney, just back in United’s side after failing to get a move to Chelsea, was caught in the head by a studs-up challenge by Vidic in a competitive training game at the club’s Carrington base on Saturday.
It left the 27-year-old requiring stitches for a gaping wound and he left at lunchtime wearing a giant bandage to cover the prominent scar.
Committed: Waynre Rooney (right) challenges Ashley Cole after coming on as substitute in Monday's 0-0 draw with Chelsea
The collision, which occurred when Rooney was trying to chest the ball, could not have happened at a worse time for the England striker.
After a summer of turmoil in which his head seemed to have been turned by Jose Mourinho, he returned to the United line-up against Chelsea on Monday and turned in a man-of-the-match performance in a 0-0 draw.
Selection problem: David Moyes' team selection has been hit by Rooney's head injury
Moyes was planning to partner Rooney and Robin van Persie for the game at Anfield — a ground where he never won with Everton. He now has to decide whether to go with a five-man midfield or push Danny Welbeck further forward to play with his Dutch ace.
Despite the rise of Manchester City, Chelsea and Arsenal, former United manager Sir Alex Ferguson always said the clashes with Liverpool were United’s biggest games of the season.
Moyes is hoping to break his summer transfer duck in the next 48 hours by bringing in Marouane Fellaini from Everton in a £23million move.
So far, United have had joint-bids for Fellaini and Leighton Baines rejected but they are prepared to concentrate on 25-year-old Fellaini if they feel Everton are more likely to let the Belgian go.
Moyes, who has failed to sign a big-name player yet in this window, is desperate to strengthen his midfield following the retirement of Paul Scholes and continuing health issues surrounding Darren Fletcher.
A late move for Real Madrid left-back Fabio Coentrao cannot be ruled out if Everton refuse to budge over the sale of Baines.