England and Northampton flanker Calum Clark will have surgery on a shoulder injury which could mean he will miss the Six Nations tournament.
Calum Clark fact-file
Born on 10 June
Joins Leeds academy at the age of 14
Becomes youngest forward to appear in the Premiership, for Leeds against Saracens
Wins a call-up to the England Under-20s; sent off in the final of the Junior World Championship against New Zealand
Signs for Northampton and captains the team, aged 21, in an LV Cup match against Saracens
Named Saints' young player of the season after making more appearances than any other Northampton player, including a start in the Heineken Cup final
Named in Stuart Lancaster's first senior England squad; banned for 32 weeks in March
The 23-year-old, who suffered the injury against Glasgow, will have surgery on Wednesday and it is unclear how long he will be sidelined.
England boss Stuart Lancaster said: "It is a shame for Calum as he had worked hard to get back into the senior squad.
"But these things happen and we'll work closely with Northampton on his rehab."
Saracens lock Mouritz Botha replaced Clark and joined up with England at their pre-tournament training camp in Leeds.
A Rugby Football Union statement said: "At this stage it is too early to speculate as to when he will return to action."
32-weeks suspended last season for breaking Leicester hooker Rob Hawkins's elbow
before the latest setback in his career.
"My shoulder needs an operation so I will be out of action for the foreseeable future. That's the game,"
Clark said on Twitter.