England forward George Kruis will see a second specialist to determine the full extent of his knee injury.
The Saracens lock is out of England's Six Nations opener against France on Saturday after suffering ligament damage during training on Tuesday.
Kruis was sent for assessment on Thursday and is not yet ruled out of the tournament, but a second opinion is now being sought.
"George will have some more assessments. We are hoping we'll know more in the next two or three days," scrum coach Neal Hatley said.
"We'll probably know a lot more after the assessment. We haven't given up on having him involved at some stage during the latter part of the Six Nations.
"We want to see what the options are moving forward. It will be the best outcome for the player, what George needs to get George right and back playing.
"The Lions or anything like that are of no significance really for us, it will be more about what George needs and what's good for George personally to make sure he's fit for the rest of the season."
In the absence of Kruis, Joe Launchbury and Courtney Lawes will make up England's second row against the French.
All 10 games of the British and Irish Lions tour to New Zealand will be shown live on Sky Sports, starting June 3 2017.