The injury suffered by George Kruis in training on Tuesday has been confirmed as a knee ligament issue, casting doubt over his involvement in England's Six Nations campaign.
Saracens lock Kruis was among 25 players retained by coach Eddie Jones for Saturday's championship opener against France, but he will now miss that fixture following further tests.
Kruis will see a specialist on Thursday to determine the extent of the problem and his estimated recovery time, but Jones is optimistic he could still play a part in the defence of England's title.
"We'll have to wait and see what the specialist's prognosis is, but we're not ruling him out of the RBS Six Nations at this stage," the Australian said.
England had been tipped to pair Kruis with Joe Launchbury in the second row against France, freeing up Maro Itoje to take the number six shirt in the absence of injured former skipper Chris Robshaw.