Maro Itoje a doubt for Six Nations opener with Ireland after suffering knee injury
Saracens say that England lock Maro Itoje will be sidelined "for a number of weeks" after suffering a knee injury.
The Gallagher Premiership leaders revealed that the 26 times-capped forward was injured on England duty.
And it is potentially a colossal blow for England boss Eddie Jones if Itoje's Six Nations participation is under threat.
England's opening game is against Ireland in Dublin on February 2, while Saracens face a number of key Heineken Champions Cup games and Premiership matches throughout December and January.
"Maro Itoje will be sidelined for a number of weeks after suffering a knee injury," Saracens said in a statement.
"The 24-year-old took a knock whilst on international duty with England, and scans have revealed a chip in his patella."
While Itoje is out of Sunday's Champions Cup clash against Cardiff Blues at Allianz Park, his England and British and Irish Lions Test colleague Mako Vunipola returns to action.
Vunipola has not played since October because of a calf strain, missing England's autumn internationals, but he will start against the Welsh side.