England and Northampton Saints flanker Calum Clark is unlikely to take part in the Six Nations after being ruled out for the "foreseeable" future with a shoulder injury.
The 23-year-old suffered the injury in his side's 27-20 Heineken Cup defeat to Glasgow Warriors at the weekend, placing his participation in serious doubt.
Clark tweeted: "My shoulder needs an operation so I will be out of action for the foreseeable future. That's the game."
The Six Nations tournament gets underway next month.
