The Premier League leaders are expecting the Ghana midfielder to return later this week to their Cobham training ground, where the club’s own medical staff will assess the state of his injury.
Ghana’s team doctor has already claimed Essien, 27, will be out of action for at least a month after suffering the injury in training.
Scans on Essien’s left leg in Luanda are understood to have shown that he has suffered a partially torn medial collateral ligament in his knee and damage to his meniscus.
A spokesperson for Chelsea confirmed: “We are aware of the injury to Michael and have been in contact with the Ghanaian national team. We will fully assess the injury on Michael’s return to us later this week. Until then we are unable to comment further.”
Essien’s injury is a massive blow to both Ghana and the Blues. Ghana were hoping he would recover from the injury to play some part in their vital Group B clash with Burkina Faso later today.
But if his injury is as bad as first feared, then Essien is likely to miss Chelsea’s Premier League encounter with Arsenal at Stamford Bridge and the opening leg of their Champions League tie against Jose Mourinho’s Inter Milan.
Ghana’s players feared the worst when Essien, who has only just recovered from a hamstring problem, went down during a training session.
“This is a big blow because Michael is so important to our team,” said striker Matthew Amoah.
“We’ve lost the motor in our midfield, and this is very bad.”
Midfielder Anthony Annon added: “Michael was turning to make a pass when he just went down. There was no contact from any other player but those around him say they heard a click.”
Essien was taken to hospital in an ambulance and underwent a scan in Luanda on Sunday. Chelsea will send the midfielder for further scans when he returns this week.
His loss will be a bitter blow to Carlo Ancelotti although the Italian coach had to play through most of December without Essien.
The Ghana midfielder has not played for Chelsea since he sustained a hamstring injury. His recovery from the setback prevented him from joining up with his international team-mates on time.
Essien began as a substitute against Ivory Coast last Friday, and will now have to sit out the crucial match against Burkina Faso later today, which the Black Stars must win if they are to progress to the quarter-finals of the African Nations Cup.
Meanwhile, England midfielder Frank Lampard believes a tactical rethink by Ancelotti has breathed new life into their title ambitions.
Lampard, who scored twice in the 7-2 thrashing of Sunderland on Saturday, insists they have now shaken off the recent poor form that saw them win just one game in five league matches.
Chelsea have scored 12 goals in their last two games after reverting to a 4-3-3 formation.
“We’ve worked on things in training and we are trying to get behind teams a bit more,” said Lampard.
“Maybe we’d become a little bit predictable. Now we’ve livened up, there is more movement in the team and you can tell by the results. The way we played against Sunderland was first class. You won’t get many better performances than that.”