Chelsea manager Luiz Felipe Scolari believes he cannot partner Nicolas Anelka and Didier Drogba together as he does not have a left-sided player.
Scolari feels that to play 4-4-2 he needs a genuine left winger but with Florent Malouda injured his options are limited.
The former Portugal boss has Joe Cole at his disposal, who has played in the position for England, but Scolari seems unwilling to deploy the 27-year-old there for his club.
Wayne Bridge could have solved the problem but the former Southampton man, who can play at full-back or left wing, has moved to Manchester City.
"I will play 4-4-2 when I have a winger who can play on the left and with his left foot," Scolari told the Evening Standard.
"When you don't have players with these characteristics it is difficult to adapt one player to play in 4-4-2.
"Florent Malouda is the only player who can play with his left foot and he is injured. Everyone else is right footed."
Scolari takes his side to Old Trafford on Sunday and is almost certain to play the 4-3-3 formation which he has adopted for most of the campaign.
This would mean that either Drogba or Anelka are likely to miss out as Chelsea look to improve their recent form of just three wins from their last 10 games in all competitions.