Chelsea goalkeeper Petr Cech will miss Sunday's home match against Everton after tearing his right calf muscle.
Cech missed 24 matches last season after fracturing his skull against Reading
Cech is almost certain to be sidelined for the Czech Republic's forthcoming Euro 2008 qualifiers against Slovakia and Cyprus.
The 25-year-old underwent a scan at Chelsea's Cobham training ground today and a small tear was revealed.
Cech suffered the injury in Tuesday's Champions League draw with Schalke 04 and was replaced by Carlo Cudicini.
Having left the Veltins Arena in Gelsenkirchen on crutches fears were raised that Cech could require surgery.
"I don't know exactly how it happened," said Cech. "I only know that I felt a pain from the 10th minute of the match.
"Nevertheless I played the first half. I feel bad that I will be out right now when myself as well as my team are both doing well."
Chelsea's club doctor Bryan English added: "It's still early but it's almost certain he will miss the game this weekend."
"We will also be liaising with the Czech FA's medical department about Petr's injury. Hopefully the international break will allow time for the injury to improve."
Cech's absence comes at a bad time for Chelsea manager Avram Grant, who is already without defenders John Terry, Paulo Ferreira and Ashley Cole.
Last season the Blues suffered a poor run of form when both Cech and Terry were out injured simultaneously and Grant will be keen for his goalkeeper to make a hasty return.
Cech, who missed 24 games last term with a fractured skull, has kept clean sheets in each of Chelsea's last six league and European games, conceding only one goal in eight.