"I am disappointed for Pat, Worcester and England because he will be sorely missed," said Robinson. "He was outstanding for us in the autumn, and he played very well in the first half for Worcester against Bristol on Friday night before coming off."
Sanderson's absence, though, suggests Lawrence Dallaglio is edging closer to an England recall. With skipper Martin Corry a certain starter at number eight against Wales, Robinson is set to select his two flankers from a quartet of Dallaglio, Lewis Moody, Joe Worsley and uncapped Sale Sharks prospect Magnus Lund.
Dallaglio has not played for England since their June 2004 defeat against Australia in Brisbane, having announced his retirement from Test rugby just two months later.
Robinson has also revealed that uncapped Leicester hooker George Chuter is unavailable for the Wales game due to a medial knee ligament sprain. But Leicester are confident Corry will be fit to lead England against Wales after the Tigers number eight sat out Saturday's Premiership draw with leaders Sale Sharks because of a rib problem.
"We made a decision that he was not quite right for the Sale game, and I felt if we played him it could have turned into one of those injuries that runs and runs," said Leicester head coach Pat Howard. "He will be okay to play in the Test match next Saturday."