George Kruis' involvement in the RBS 6 Nations is in doubt, with the England lock due to see a specialist on Thursday after suffering a knee ligament injury which will see him sit out the side’s opener against France.
Kruis was given the all-clear to face France last week after recovering from a fractured cheekbone, but was forced to miss training on Tuesday after sustaining the injury.
The 26-year-old’s participation in the remainder of the tournament remains unclear.
England coach Eddie Jones said: "We'll have to wait and see what the specialist's prognosis is, but we're not ruling him out of the RBS 6 Nations at this stage."
If Kruis is ruled out, Courtney Lawes and Joe Launchbury will reform the second row partnership that started against South Africa and Fiji during the autumn.
Speaking earlier on Wednesday, assistant coach Paul Gustard said he was confident England could cope if Kruis is absent.
"We pride ourselves as a nation about the quality we have around the country," he said.
"As a coaching group from day one we were very excited about the talent we've got in English rugby at the moment.
"We're proving we can cope with people not being in the team and while there are people missing in this Six Nations there are also people returning and that's also exciting. The likes of Maro Itoje and James Haskell coming back into the group is encouraging."
Itoje, the dynamic 22-year-old, who missed the autumn internationals with a hand injury, will move from lock to fill the void at blindside flanker created by Chris Robshaw's championship-ending shoulder surgery.
Haskell, following his seven-month absence with a toe injury, is set for a return to the bench.
England, on a 14-match winning run, will start the tournament as favourites to defend their title. But Gustard insists their sole concern is victory against France on Saturday.
"All we want to do is go out and win," Gustard added. "Our entire focus since 1 January, even before that since we beat Australia at Twickenham, is to beat France.
"That's all we've spoken about as a coaching group, all the players have been speaking about. We're excited about the challenge and getting the right result.
"France are a very good team. We saw progress from them in the autumn and they ran a couple of teams close.
"Traditionally, they have got a very strong pack. They've got a big heavy tight five and backs who can play with verve and when the ball comes loose and alive they find another gear. From that, we have to respect them."
Live Six Nations coverage of Scotland versus Ireland on RTÉ Two from 1.30pm on Saturday (KO 2.25pm) and live radio commentary on RTÉ Radio 1’s Saturday Sport programme from 2pm.
Live coverage of Scotland v Ireland in the Women’s Six Nations on RTÉ Two from 6.30pm (KO 6.35pm) on RTÉ 2, with live radio updates and reaction on an extended 2FM Game On programme at 7pm.
Live coverage of Scotland v Ireland in the U20's Six Nations on RTÉ Two from 8.15pm (KO 8.30pm)
