The Warriors flanker, England's outstanding forward during their autumn defeat against New Zealand, will miss appointments with Wales, Italy and Scotland.
He was hurt during Worcester's Guinness Premiership victory over Bristol on Friday night in his comeback game after being sidelined for more than a month because of back trouble.
Sanderson's absence - he will be sidelined for between four and six weeks - seemingly edges Lawrence Dallaglio nearer an England recall.
Dallaglio, back in the England squad after retiring from Test rugby 17 months ago, is battling for a starting berth against Twickenham visitors Wales next Saturday.
With captain Martin Corry a certainty to start at number eight, England head coach Andy Robinson is set to select his two flankers from Dallaglio, Lewis Moody, Joe Worsley and uncapped Sale Sharks prospect Magnus Lund.
"I am obviously gutted," said Sanderson. "I felt things went well for me in the autumn and I had worked hard to get back for last week.
"But you have to accept these things happen in rugby, and I am just looking forward to getting fit for Worcester, and hopefully England."
Coach Andy Robinson added: "I am disappointed for Pat, Worcester and England because he will be sorely missed.
"He was outstanding for us in the autumn, and he played very well in that first-half for Worcester against Bristol before coming off. I am looking forward to welcoming him back into the squad."
Robinson also revealed that uncapped Leicester hooker George Chuter is unavailable for the Wales game due to a medial knee ligament sprain.
"George has been playing consistently well for Leicester, and he was certainly pushing to be in the 22. It is unfortunate for him," said Robinson.
Leicester, meanwhile, are confident Corry will be fit to lead England against reigning Six Nations champions Wales.
The Tigers number eight sat out the Guinness Premiership draw with leaders Sale Sharks because of a rib problem, but that appears to have been a precautionary move ahead of the England squad assembling at their Surrey training base.
"Corry is one for the England medical team to deal with," said Leicester head coach Pat Howard.
"We made a decision that he wasn't 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.
"He will be okay to play in the Test match next week."