Ghana midfielder Michael Essien is out of the 2010 Africa Cup of Nations after suffering a knee injury in training.

The Chelsea player could also miss Premier League and Champions League matches after he suffered a partially torn medial ligament in his left knee. Ghana's team doctor believes the injury will keep the 27-year-old out for at least a month and possibly longer.

The Black Stars, who had been keen to field Essien for Tuesday's crucial Group B tie against Burkina Faso, commented: "This is a big blow because Michael is so important to our team," striker Matthew Amoah told BBC Sport. "We've lost the motor in our midfield, and this is very bad."

The Chelsea man only returned to training on 6th January, having not played since tearing his hamstring while on Champions League duty with his English club in early December. Essien becomes the latest of Ghana's key men to suffer injury, with John Pantsil, John Mensah, Laryea Kingston and Stephen Appiah all ruled out before the tournament.