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.
England flanker James Haskell insists he will be pushing as hard as possible to be back from a toe injury in time to make his case for a spot in Eddie Jones' side looking to defend their RBS 6 Nations title next year.