The 28-year-old Ghana international, who missed much of the 2008/2009 campaign after sustaining anterior cruciate ligament damage, will now be assessed by the club's medical staff before any further prognosis.
"Michael Essien suffered an injury to his right knee during training this week," said a statement on the club's website, www.chelseafc.com.
"He will undergo tests over the next few days to determine the extent of that injury. Until we have the full results of those tests we will not be commenting further."
Essien missed the 2010 World Cup because of a knee problem, and the midfielder's fresh injury represents an early 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.
Source: AFP
Source: AFP