CHELSEA could be without Michael Essien for their crunch title showdown with Arsenal next month.
The Ghana midfielder is currently in Angola for the African Nations Cup but looks set to miss the rest of the tournament after suffering a knee injury in training.
Scans revealed Essien has a partially torn medial collateral ligament in his left knee and damage to his meniscus.
And Ghana's team doctor believes the 27-year-old will be out of action for at least a month.
Essien's team-mate Michael Amoah said: "This is a big blow because Michael is so important to our team.
"We've lost the motor in our midfield, and this is very bad."
Midfielder Anthony Annan 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, and then the physios rushed over."
Essien was taken to hospital in an ambulance and underwent a scan in Luanda on Sunday.
His loss will be a bitter blow to Carlo Ancelotti, although the Italian coach had to play through most of December without Essien.
The midfielder has not played for the Blues since he sustained a hamstring injury.
His recovery from the setback prevented him from joining-up with his international team-mates on time.
Premier League leaders Chelsea face the Gunners on February 7 at Stamford Bridge and it is understood Essien could also miss games against Hull and Everton.
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."
The Ghana midfielder is currently in Angola for the African Nations Cup but looks set to miss the rest of the tournament after suffering a knee injury in training.
Scans revealed Essien has a partially torn medial collateral ligament in his left knee and damage to his meniscus.
And Ghana's team doctor believes the 27-year-old will be out of action for at least a month.
Essien's team-mate Michael Amoah said: "This is a big blow because Michael is so important to our team.
"We've lost the motor in our midfield, and this is very bad."
Midfielder Anthony Annan 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, and then the physios rushed over."
Essien was taken to hospital in an ambulance and underwent a scan in Luanda on Sunday.
His loss will be a bitter blow to Carlo Ancelotti, although the Italian coach had to play through most of December without Essien.
The midfielder has not played for the Blues since he sustained a hamstring injury.
His recovery from the setback prevented him from joining-up with his international team-mates on time.
Premier League leaders Chelsea face the Gunners on February 7 at Stamford Bridge and it is understood Essien could also miss games against Hull and Everton.
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."