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The Ghana Football Association (GFA) has expressed its sadness over the injury suffered by Michael Essien.

The Chelsea and Ghana midfielder was training in England this week when he sustained the right knee injury.

Further tests will reveal the severity of the injury.

"The GFA and Ghanaians express their sympathy to Michael Essien in this difficult time and remain hopeful that, further tests would not rule him out for long," a GFA statement read.

"We stand by him and wish him a full and speedy recovery.

"The GFA is going to follow his progress closely to have news of his recovery."

The 28-year-old was ruled out for more than six months in 2008 when he sustained cruciate ligament damage.

Essien also missed the 2010 World Cup because of a knee problem, and the midfielder's latest setback is a blow to new Chelsea manager Andre Villas-Boas, who is preparing his squad for their trip to the Far East, where they will compete in the Asia Cup.

Essien joined the Blues from French club Lyon in 2005 in a £24.4m deal and has gone to to establish himself as a key player at Stamford Bridge.

He has helped Chelsea to two Premier League titles and three FA Cups, as well as the Carling Cup in 2007.

Despite being ruled out for the majority of the 2008-09 campaign, Essien has amassed 229 appearances for the London side, scoring 26 goals.

While the club have not elaborated on the severity of the problem, Essien will be mindful of what happened to him while playing for Ghana in a World Cup qualifier against Libya three years ago.

On that occasion he landed awkwardly during the match and was subsequently told he faced a lengthy spell on the sidelines.