Carlo Ancelotti faces a nervous wait to discover how long he will be without Michael Essien after the Ghana midfielder limped off with a hamstring injury during Chelsea's 2-2 draw against APOEL Nicosia.
Blues boss Ancelotti was already frustrated after watching his side fail to win for the third successive match thanks to a sloppy display capped by John Obi Mikel's costly mistake.
And the prospect of being without Essien, one of the few Chelsea stars to emerge with any credit from Tuesday's Champions League draw with the Cypriot champions, ensured he left Stamford Bridge in a foul mood.
The Italian admitted Essien, who limped off soon after scoring a thunderous first half equaliser, is certain to miss Saturday's home game against Everton and a scan on Wednesday will reveal if the midfield tyro will be sidelined for much longer.
"Michael has a problem with his leg. We will look at him over the next few days and check on him on Tuesday," Ancelotti said.
"We hope it's not a big problem. I think he will not be able to play on Saturday."
Essien's injury couldn't have come at a worse time for a team suddenly looking surprisingly fragile.
Since winning at Arsenal 10 days ago, Chelsea have been knocked out of the League Cup at Blackburn, suffered a 2-1 defeat at Manchester City in the Premier League, and now seen the unheralded minnows from Cyprus end their club record 12-match winning run at the Bridge.
While the result did no damage to Chelsea's European challenge as they had already qualified as Group D winners, the lacklustre manner of their performance drew an angry response from Ancelotti.
For the first time in his six-month reign at Chelsea, the former AC Milan boss let rip at his players for falling below the standards he expects.
"I am unhappy. We went a goal down and we did a good reaction, scored two goals and played with intensity. But the second half was totally different," he said.
"We lost concentration, had no intensity and played too slowly, too soft. We have to play for 90 minutes with intensity and concentration.
It's a psychological thing. The result isn't important because it's important to play our best in every game.
"This was not how we want it. I spoke with my players about it afterwards.
"The first goal can happen, the second one no. It was the consequence of our soft play. We had the possibility to close the game out but didn't play well."
The only bright spot for Ancelotti was an accomplished first start from French midfielder Gael Kakuta, the 18-year-old whose controversial transfer from Lens threatens to land Chelsea with a two-year transfer ban for inducing him to move.
Kakuta offered a tantalising glimpse of why he is regarded as the brightest talent in Europe when he embarked on an incisive run before playing a perfectly weighted pass for Yuri Zhirkov, whose cross was converted by Didier Drogba for Chelsea's second goal.
"Kakuta is the only one who could think. He played well," Ancelotti said. "He showed his talent and made a fantastic pass for the second goal.
"We have to look at him and stay calm but he will be the future of Chelsea."
The Blues never looked comfortable from the moment Marcin Zewlakow slotted in a Constantinos Charalambides cross in the sixth minute as John Terry appealed in vain for offside.
Essien and Drogba put Chelsea in front but APOEL deservedly snatched a draw in the 87th minute when Mikel's backpass to Terry fell short and Nenad Mirosavljevic nipped in to slide hom the equaliser.
APOEL coach Ivan Jovanovic said. "It's a very important result drawing with one of the top teams in Europe.
"In a game like this we knew we wouldn't have many chances and we've been lucky that we were able to score twice in five or six chances."