Will Greenwood has joined his England midfield colleague Mike Tindall in facing a race against time to make the world champions' RBS 6 Nations Championship opener against Wales.
Harlequins centre Greenwood, capped 55 times, underwent a shoulder operation on Wednesday.
"Will underwent a scope on a long-standing shoulder problem, and although we are still waiting to hear from the consultant on how the operation went, he will clearly be out for a minimum of four weeks, maybe longer, depending on the results," said Quins team manager Mike Scott.
The anticipated minimum lay-off would sideline Greenwood until January 20, and given that Quins are already out of the English Cup - January 22/23 is quarter-final weekend - he would then have only one scheduled game to prove his fitness before the February 5 Wales clash.
Greenwood has struggled for form this season, and was on the bench throughout England's autumn series of Tests against Canada, South Africa and Australia.
But the 32-year-old boasts an outstanding try-scoring record against Wales, and England head coach Andy Robinson might have been tempted to start with him at the Millennium Stadium.
Tindall, meanwhile, is battling to overcome a foot injury that early forecasts suggested would not heal in time for the Cardiff showdown.