Chelsea could be facing more injury problems in central midfield, after Michael Essien suffered an injury on international duty last night.

The Ghanaian limped out of his country's 1-0 defeat to Libya in the 22nd minute as a result of a cynical tackle.

"My injury? It is serious but I can be ready again soon," Essien told skysports.com.

Essien will have the injury assessed by Chelsea's medical staff, with some reports claiming he could be out for four weeks—ruling him out of the crucial game with Manchester United on September 21st.

The Blues are already short of numbers in the middle of the park, with John Obi Mikel and Michael Ballack also injured.

Mikel should be back for the game against Manchester City next weekend, although Ballack's chances appear to be slimmer.