Ghanaian midfielder Michael Essien is to undergo tests to establish the extent of his knee injury sustained in the African Cup of Nations.

The Chelsea star picked up the injury in training and is already expected to miss key club games in the next few weeks.

Essien had just returned to fitness following a hamstring injury when he went down while passing the ball.

Ghana team-mate Anthony Annan said: "There was no contact from any other player, but those around him say they heard a click and the physios rushed over."

Chelsea has said the player is returning to England to have the knee assessed amid fears that it could be a medial ligament problem that could keep him out of action for a significant period of time.

Those dealing with a knee injury may find that ultrasound treatment aids recovery.

One footballer whose knee has turned out not to be as bad as feared is Manchester United striker Dimitar Berbatov.

The Bulgarian - who may have to have an exploratory operation on the joint - suffered a knock in the game against Burnley at the weekend but it turned out to only be a dead leg.