Courtney Lawes is in danger of missing the remainder of England's RBS 6 Nations championship with a shin injury.
The Northampton lock made his first appearance of the championship off the bench in last weekend's 19-12 defeat to Wales after overcoming a knee injury.
But Lawes was sent for a scan after complaining of shin shoreness in his right leg and specialists have discoverd an "inflammation of the tibia".
Lawes has been advised to keep the weight off his leg and he is expected to be sidelined for weeks rather than days.
England play France in Paris a week on Sunday and end their Six Nations campaign at home to Ireland on March 17.
England's interim head coach Stuart Lancaster said: "It's unfortunate for Courtney as he had just really got back into training with us but we have to listen to expert medical opinion. If that means he has to keep the weight off his right leg to help him recover then we have to respect that and work with Saints to manage his recovery."
Lawes made an impact for England off the bench against Wales but his one mistake proved crucial, when Wales centre Scott Williams robbed him of the ball and broke away to score.
England number eight Ben Morgan has been ruled out of the Scarlets' RaboDirect PRO12 game against Connacht on Friday night by a calf strain.
Lancaster was forced to release Morgan back to the Scarlets against his wishes due to International Rugby Board regulations.
Owen Farrell, who missed training on Wednesday through illness, was involved in Thursday's sessions at Loughborough but Chris Ashton sat it out as he recovered from sickness.