Chelsea midfielder Michael Essien is undergoing tests after suffering a potentially serious knee injury during training last week.Essien, 28, missed six months of the 2008/09 season due to an anterior cruciate ligament sustained on international duty for Ghana.
Knee problems also kept him out of the 2010 World Cup in South Africa.
Chelsea are not willing to discuss the severity of the former Lyon man’s injury until the tests have been completed.
“People have been speculating about the extent of the injury, but it is dangerous to jump the gun,” the club said in a statement.
“Michael will be sent away for tests over the weekend and we will not be commenting further until the results of those tests are known.”
“We want to make sure we have the full picture and I don’t think we will know how serious it is until Monday at the earliest.”
Essien may be ruled out of Chelsea’s pre-season tour of Asia, starting against a Malaysia XI on July 21.
He could also be in doubt for the beginning of their first English Premier League campaign under new manager Andre Villas-Boas, with Chelsea kicking off away at Stoke City on August 13.
The west London outfit have also confirmed Michael Emenalo will move from his role as assistant first-team coach to become sporting director at Stamford Bridge.
The 45-year-old Nigerian succeeded Ray Wilkins as first-team coach in November 2010.
“Without delving too deeply into it, the first thing is that I’m going to be supporting the manager and working with him in making sure that things run smoothly,” Emenalo said.
“I have the responsibility to direct and manage our scouting structure internationally and domestically, and to keep an eye on and assist the progress of the academy. That’s the simple summation.”