England number eight Billy Vunipola has been ruled out of the remainder of the RBS 6 Nations with an ankle injury.
Vunipola limped off in the second half of Saturday's 13-10 victory over Ireland and will now miss the final two games against Wales and Italy.
"It's a blow as Billy has had a good Six Nations but he is young and will be back," head coach Stuart Lancaster said.
Vunipola sprained his right ankle at Twickenham and a scan on Monday afternoon revealed the extent of the ligament damage.
It is not known how much more of the season the Saracens back row will miss.
Ben Morgan replaced Vunipola against Ireland and will be promoted to the starting line-up for the visit of Wales on Sunday week.
Either Tom Johnson or Matt Kvesic will take Morgan's place on the bench.
"The encouraging thing is that we have Ben Morgan and other back rows such as Matt Kvesic and Tom Johnson who are all competing hard for places," Lancaster said.
Joe Launchbury's remarkable display of endurance in Saturday's victory over Ireland was among the highlights of a potentially defining Red Rose performance under Lancaster.
When the final whistle sounded after 80 minutes of compelling and nerve-shredding action, the spent Wasps lock could only place hands on knees and bury his head in the chest of team-mate Henry Thomas.
Launchbury's tank-emptying shift typified the commitment of an England pack that he declares will run themselves into the ground to break the will of their opponents.
"The key is that in every international you try to get yourself into that place of exhaustion. That's what enables us to win games," Launchbury said.
"We pride ourselves on being a pack who can play this all-court game and can run around and take teams to dark places.
"That's what we tried to do against Ireland and obviously it's hard work on ourselves, but hopefully you see the impact it makes on the opposition as well."
Launchbury was a repeated thorn in Ireland's side at the breakdown and made 15 tackles - the second highest in both teams and only one behind Chris Robshaw.
It was the closing moments that produced his finest achievement, clipping the ankle of Dave Kearney with an outstretched arm as the Ireland wing threatened a repeat of the late agony endured against France three weeks ago.
"Not at all was I sure I was going to make it. I was probably a bit out of position," said Launchbury, who was switched to blindside flanker in the 70th minute to accommodate replacement lock Dave Attwood.
"I've tried to chase down wingers in the past but I'm pretty sure that's the first tap-tackle I've ever tried.
"My head was down on the turf, face down. I think that's the first time I've ever managed to get the guy down."