The London Wasps flanker hobbled off during the early stages of England's defeat to New Zealand at the weekend and had been anxiously waiting to find out the extent of the damage to his right knee.
A series of scans revealed a medial collateral ligament injury, with both Wasps and the RFU seeking further medical advice.
It has now been decided that the 32-year-old will not have surgery but he will need to undergo extensive rehabilitation with the hope of returning to the game by the end of January next year.
"After a consultation with London Wasps' knee surgeon, Andy Williams, it has been decided by all parties that, in preference of surgery, Joe will take a conservative approach to his rehab to repair the Grade 3 medial collateral ligament injury to his right knee," read a statement from Wasps.
"Joe is expected to be out for a minimum period of eight weeks.
"London Wasps and the England medical team will continue to work together on Joe's recovery."
As a result, Worsley's place in the England line up for the first game of the 2010 Six Natiosn is in severe doubt, with Martin Johnson's men facing Wales at Twickenham on February 6.
The World Cup winner had only just returned to the England starting XV having missed the loss to Australia through injury and then been among the replacements for the narrow win over Argentina.