Maro Itoje could be a doubt for England's Six Nations opener in Italy after Saracens confirmed he fractured his jaw against Harlequins.
Itoje was taken to hospital for scans after being taken off in the 48th-minute of his side's 20-19 defeat at the Stoop Sunday with blood pouring from his mouth.
Those scans confirmed the fracture, with a Saracens statement revealing the England forward would see a second specialist this week to confirm a timeframe for his return.
The exact timescale of that recovery remains unclear, but Itoje looks set to miss his side's back-to-back Champions Cup clashes with Clermont.
His Saracens teammate George Kruis returned to training three weeks after he fractured his cheekbone last December but did not feature in the Six Nations due to a subsequent knee injury.
Itoje's England and British & Irish Lions colleague Anthony Watson was ruled out for almost three months with a broken jaw at the end of 2016, meanwhile.
A similar recovery period would put Itoje in a race against time to be fit for England's opening Six Nations match against Italy in Rome on Feb. 4.
"Scans have confirmed that Saracens forward Maro Itoje fractured his jaw in Sunday's round 10 Aviva Premiership clash against Harlequins," the Saracens statement read.
"The 23-year old England forward left the field in the 48th minute of Saracens' 20-19 defeat at the Twickenham Stoop and was taken to hospital where scans confirmed the fracture.
"Itoje will now see a second specialist later this week to confirm his return to play schedule."