Manchester United manager Louis van Gaal said on Friday that injuries to key players had left him with the "worst possible scenario" ahead of their crunch clash with Premier League leaders Chelsea.
Third-placed United will travel to London without influential midfielder Michael Carrick (calf) plus key defenders Marcos Rojo (stomach), Phil Jones and Daley Blind (both ankle) as they seek to close an eight-point gap with Chelsea at Stamford Bridge on Saturday.
Van Gaal confirmed the quartet all suffered injuries during last Sunday's 4-2 derby win over faltering champions Manchester City.
United's injury problems mean their Dutch manager may have to deploy striker Wayne Rooney in midfield, having used the club captain there earlier in the season.
"It is the worst possible scenario," van Gaal told a news conference on the eve of the match. "So I have to change my line-up a lot against Chelsea.
"Michael Carrick is injured, he cannot play. But not only Carrick - Daley Blind, Phil Jones and Marcos Rojo cannot play. They are all (injured) from the game against Manchester City
"It cannot be worse because it's two players in the left central defensive positions, and Jonny Evans is still suspended.
"Blind and Carrick play in the holding position in midfield, I don't have any other player, or Wayne Rooney can play in the position."
Van Gaal added: "It's because of the distance between the matches. Blind and Jones were very close to playing but it was not enough."
"Other players can take profit of the moment now. It's always like that. It's not special in the life of a manager or a team."
Despite the casualty list Van Gaal hinted, however, that striker Robin van Persie could feature after he stepped up his return from an ankle problem, while left-back Luke Shaw should be available following hamstring trouble.
"Shaw has trained already so he can play," the manager explained."Van Persie is another story. This is the first week he's trained with the first team, but maybe we have to think about him."
'Bigger than big'
Chelsea, as well as an eight-point advantage over United, also have the luxury of a game in hand.
Van Gaal acknowledged it would probably be asking too much to overhaul Jose Mourinho's side, whom he said would be happy to take a point out of the game, and win the Premier League title.
"It is not logical but it is possible (to win the title)," he said. "The challenge is bigger than big. It will be very difficult.
"It's 'when and if', and I don't believe in 'when and if'. I believe in facts. We are behind Chelsea. We have to play against them and so do Arsenal so we can lay pressure on Chelsea's shoulders.
"I think that Chelsea will be satisfied with a draw. They will want to beat Manchester United and we want to beat them, the question is how long players can play with discipline.
"Of course we'll be confident. It's not only one line-up that we can play our philosophy so we have a lot of confidence now."
Van Gaal insisted he shared the same hunger as Chelsea manager Mourinho, his protege when he was first in charge of Barcelona in the late 1990s, to win silverware, but also derived satisfaction from the development of players.
"We live for these titles...That is the only satisfaction that you have as a manager, that you have a title," he said.
"If you are second or third, OK, you can play in the Champions League, but a title is more fixed for you. It comes with your name. That is why managers are fixated on titles. When you reach that goal you are happy.
"But to be involved in the game and to reach a goal with young people, that is also a goal for me. That is why I am still a manager.
"I don't have to work anymore," the 63-year-old added. "You can count on that. But I like to work with young people and to help them in their career."