Fears that prop Alex Corbisiero could miss the entire Six Nations have forced England to call up Henry Thomas.
Corbisiero underwent a procedure on Wednesday to clear out a "loose body" in his knee and London Irish director of rugby Brian Smith would be surprised if he is available inside 10 weeks.
The initial prognosis from England coach Stuart Lancaster was that Corbisiero would miss the first two games, but Smith fears it could be much longer and that he might not even play again this season.
"Unfortunately for Corbs he had further surgery. The information our medical team have been given is that it is likely to be a 10-week injury," Smith said.
"I'd like to think he could get back on the park for us before the end of the season. There are still major question marks about that. He has a significant injury and he needs to be managed well."
Sale front-rower Thomas will train with England at their Pennyhill Park base ahead of Saturday's Six Nations opener against Scotland at Twickenham.
Harlequins back Ugo Monye will also train with the squad while Gloucester's Freddie Burns stays with his club for treatment on a knee injury.
Prop Shaun Knight has withdrawn from the England Saxons squad as he, too, must return to Gloucester due to a knee injury.
The Saxons convene in Newcastle on Monday morning ahead of their match with Scotland A at Kingston Park on Friday.