Barritt, Burrell doubts for England
Brad Barritt and Luther Burrell are England's latest injury concerns, handing boss Stuart Lancaster a serious shortage at centre ahead of next weekend's Six Nations opener in Cardiff.
Saracens centre Barritt is battling a knee injury while midfielder Burrell suffered a concussion in Northampton's chastening 32-8 weekend loss at Racing Metro.
The England squad convened at Pennyhill Park on Monday night, with Jonathan Joseph and Billy Twelvetrees the only fit centres.
Leicester wrecking ball Manu Tuilagi has been omitted from England's training squad and may miss the entire Six Nations as he continues to fight back from groin injury.
England retain the hope Burrell will return to training on Friday, while Barritt's knee, Kyle Eastmond's shoulder and Owen Farrell's knee require further assessment.
"The players will be fully assessed once they get into camp this evening and it's too early to give any definitive news on their status," said head coach Lancaster.
"Owen's (Farrell) knee has been scanned. Owen will see a specialist this evening and we will be able to provide an update on him and the other injury players tomorrow, along with any other potential additions to the squad."
England boss Lancaster has said it would be a "big, big ask" for rugby league convert Sam Burgess to feature in the Six Nations.
The big-money Bath recruit starts his Rugby World Cup fast-tracking in England Saxons' Friday night clash against the Irish Wolfhounds in Cork.
Any more midfield injuries however, and the 26-year-old could find himself elevated to the senior squad by default.
"Sam is certainly more than capable, his performance against Wasps at The Rec suggests he's more than capable of playing international rugby," said Saxons head coach Jon Callard of Burgess.
"We'll know probably a little more after Friday night.
"I would have thought if I was a betting man, the seniors would want him to start (against the Irish Wolfhounds).
"The challenge for us is to get the best out of him, and all the other players as well.
"We've got to give them that opportunity to show what they can do.
"I think Bath have handled him beautifully: they've given him the experience, slowly put him into a European Cup situation, and given him that.
"And this is the next stage of his development.
"We're all excited for Sam, but we're just taking it very, very calmly.
"He's still potentially got three World Cups in him.
"So I think there's still plenty of time."
British and Irish Lions flanker Tom Croft and Northampton lock Christian Day have also joined the senior training squad from the England Saxons, to offset injuries from the weekend's Champions Cup matches.
Croft slots in as cover for Tom Wood, who is battling ankle trouble, and Day has moved up as a result of Geoff Parling's knee injury.
England will continue to monitor the progress of both Wood and Parling.
Carl Fearns and James Gaskell have replaced Croft and Day in the Saxons squad, as England's second string gear up to face the Irish Wolfhounds in Cork on Friday night.
Leicester flanker Croft has not played for England since the record 30-3 defeat to Wales in Cardiff that handed Warren Gatland's men the 2013 Six Nations title.
The 29-year-old beat severe neck problems only to be laid low again by a knee injury, but is finally clawing his way back to fitness.
Forwards coach Graham Rowntree had admitted England need to "find a way" to bring Croft back into the equation, but his elevation back to the full squad has come sooner than anticipated.
"He's missed quite a bit and there have been some question marks about the injuries and bringing him back to full fitness," said Saxons coach Callard.
"But Tom's a great footballer, and if an opportunity presents itself I'm sure he'll take it.
"He's a great athlete and the more he plays now the more we'll see him back to his best and showing exactly what he can do."