Chelsea midfielder Michael Essien has sustained a knee ligament injury in the 3-2 English Premier League win over Birmingham City, and is a doubt for Thursday's (AEST) trip to Reading.
After a pre-season scarred by injuries to a host of key players, including captain John Terry, coach Jose Mourinho must have thought things were looking up as Didier Drogba made a quicker than expected return to fitness against Steve Bruce's side.
Instead, he could be facing a spell without his most versatile player.
Essien's value was underlined against Birmingham. He capped a dynamic display with the winner that ensured Chelsea extended its unbeaten run in league matches at Stamford Bridge to 64, beating Liverpool's previous top-flight record.
"It was something in the knee ligament," said Mourinho.
"He (Essien) was limping and the doctor was saying he was in pain.
"I had two midfielders on the bench so I made the change immediately. If you ask me if he is ready for Wednesday I don't know."