Chelsea boss Jose Mourinho has revealed Samuel Eto'o will undergo medical tests on Wednesday to determine the severity of his injury, reports the Daily Mail.
The 32-year-old had to be stretchered off in the 42nd minute of Chelsea's clash against Basle due to a muscle injury in his left leg.
Cameroon international Eto'o, who was replaced by Fernando Torres, seemed to have strained his muscle while chasing the ball.
The former Anzhi Makhachkala looked in extreme discomfort while calling for help from Chelsea's medical team.
Mourinho said on Eto'o's injury: "Samuel has a muscular injury.
"We'll have to wait for the scans. Clearly I've got signs of fatigue and players who have trouble playing two matches in three days. We paid the price today of the international week."
Chelsea went on to lose the Group E encounter 1-0, but sealed qualification to the last 16 of the Champions League due to Steaua Bucharest's goalless draw with Schalke.
Stamford Bridge boss Mourinho will be hoping Eto'o, who has scored four goals in 14 games since moving to Stamford Bridge, can make a quick recovery from his latest injury.
Chelsea host Southampton at home on Sunday before travelling to the north-east to play Sunderland next Wednesday.