Manchester United will be without midfielder Nicky Butt for their Champions League clash with Olympiakos on Wednesday.
The United squad flew out today without the England star, who was ruled out with an ankle injury that is baffling the club's doctors.
Top scorer Ruud van Nistelrooy, who has suffered recurring hamstring problem, was already ruled out of the group F clash with the Greek champions.
Alex Ferguson admitted the club were still unsure as to the exact nature of Butt's injury but indicated he was almost certain to miss Saturday's home game against Aston Villa.
But Ferguson is hopeful van Nistelrooy will be fit by the weekend and that England defender Rio Ferdinand, who had knee surgery earlier this month, could make his return against Villa.