England are facing a potential crisis at loosehead prop ahead of Saturday's clash with New Zealand with Alex Corbisiero a doubt for the game.
The Northampton prop, a hero of the British & Irish Lions series victory in Australia, faces a key training session on Tuesday afternoon that is likely to decide whether he can take on the All Blacks at Twickenham.
Corbisiero missed the first QBE International with Australia but did take part against Argentina but his knee is continuing to cause him problems.
With Mako Vunipola ruled out with his own knee problem and Joe Marler following return to play protocols for concussion, England could face world champions New Zealand with all three senior looseheads missing.
If none of them can play Wasps' prop Matt Mullan will be pitched into the biggest match of his life for his second cap.
"We're monitoring Alex now. He's normally a one session per game player, especially on a Tuesday when we do two heavy sessions," forwards coach Graham Rowntree said.
"We're currently monitoring him to see what he's able to do this afternoon, as we are with a couple of other players.
"We'll know more after we've monitored him this afternoon. As far as I'm concerned we're still as we are for the weekend."
Corbisiero saw his knee specialist in a routine meeting on Monday evening.
"Seeing a specialist is part of Alex's ongoing situation with his knee. A lot of our players are seeing specialists all the time," Rowntree said.
"It's nothing out of the ordinary, it's part of his knee management in conjunction with Northampton and our team physios."
Marler was concussed in the 31-12 victory over the Pumas, but it is hoped he will be available for the climax to the QBE Internationals. If Marler is ruled out, Rowntree confirmed Mullan will start.
"Joe's following the concussion protocols. He didn't train this morning, but we're expecting him train properly on Thursday," Rowntree said.
"We were able to scrummage properly this morning because we've had Matt Mullan with us for two days.
"He's played very well this season and is able to step right in if we have any concerns."
Watch England take on the All Blacks on Sky Sports 1 on Saturday, with coverage beginning at 1.30pm.