Steve Borthwick is expected to be sidelined for up to a month after a kick to the face from Gloucester hooker Olivier Azam left him with "extreme swelling" around his right eye.
The England captain was admitted to Moorfields Eye Hospital last night and will undergo further tests today to establish the full extent of his injury.
Borthwick is set to be out of action for between two and four weeks, but any longer than that and he could be a doubt for England's opening autumn international against Australia on November 7.
The Saracens medics had no immediate concerns over Borthwick's sight but he required five stitches after the incident early in Saracens' 19-16 victory.
Azam insisted after the game that any contact had been accidental, but Saracens have studied their own video footage of the incident and head coach Mark McCall fears otherwise.
McCall said: "We have had a quick look at it. We are concerned at the way it occurred and it would appear it may have been a deliberate act of foul play.
"Steve is at hospital to see if there is any damage to his eye-socket.
"It is more than a cut. His eye is completely closed over and at this stage we don't know how badly damaged it is.
"The video footage we have seen so far would appear to be reasonably clear.
"It is something nobody wants to see. Steve was on the ground and pretty much defenceless in the position he was in."
Azam explained he had lashed out with his right leg because his left ankle was being twisted at the bottom of a ruck and that he was not aware he had even made contact with Borthwick.
"I didn't know I did it. Someone twisted my ankle but I didn't know I touched him. Of course (it was accidental)," he said.