"I will play 4-4-2 when I have a winger who can play on the left and with his left foot," Scolari said in 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."
Wayne Bridge, sold to Manchester City at the weekend, would also have offered a solution but is no longer an option.
Scolari has favoured a 4-3-3 formation but Chelsea have won only three of their last 10 games ahead of the Premier League clash against champions Manchester United at Old Trafford this weekend.
Meanwhile, striker Ben Sahar has joined Dutch side De Graafschap on loan until June 30.