England lock Courtney Lawes will miss "the first few weeks" of the Six Nations because of an ankle injury, Northampton Saints director of rugby Jim Mallinder has announced.
Lawes will have an operation on Monday morning and is not expected to miss the entire Championship, but is definitely out of the crunch opening fixture against Wales in Cardiff on February 6.
Mallinder, speaking after Northampton's 20-9 European Champions Cup victory over the Ospreys in Swansea, said Lawes suffered the injury during Saints' Aviva Premiership clash against Leicester just before Christmas.
He has not played since that game, and now the full extent of his injury has been confirmed.
"Courtney, unfortunately, has not recovered from his ankle injury," Mallinder said. "He will be going in for a little operation on Monday.
"He has got a little bit of bone that he just needs clearing out, so he is going to miss the first few weeks of the Six Nations, as well as missing next week [when Northampton face Racing Metro].
"It is just a little bit of bone that chipped off in the Leicester game. He would be expected to get back [playing] while the Six Nations is still going on.
"It is a blow for us because we haven't got him for next week, and it is a blow for him and England because he is a key player."
England's lock stocks have already been depleted by the loss of Wasps' Joe Launchbury, who will miss the entire season, although Leicester's Geoff Parling, who was ruled out of the autumn series with concussion, returns. No.8 Ben Morgan was ruled out with a broken leg last weekend.
Stuart Lancaster will name his England squad for the Six Nations on Wednesday.