England forward Maro Itoje could miss the start of the Six Nations after fracturing his jaw playing for Saracens.
Itoje left the field during his club's loss to Harlequins on Sunday in the English Premiership after picking up the injury following a collision with England team mate Mike Brown.
"Scans have confirmed that Saracens forward Maro Itoje fractured his jaw in Sundays round 10 Aviva Premiership clash against Harlequins," his club said in a statement on Tuesday.
"Itoje will now see a second specialist later this week to confirm his return to play schedule."
Similar injuries have ruled players out for about two months and England coach Eddie Jones faces a nervous wait with his team's opening Six Nations match against Italy on 4 February.
Itoje played every game in England's victorious 2017 Six Nations campaign and three tests for the Lions as they drew with New Zealand.
He was nominated for the World Rugby Player of the Year award.