Williams was forced from the field at half time after falling awkwardly in a heavy tackle from Racing Metro centre Francois Steyn.
His shoulder dislocated and then immediately returned back into place but Williams must now undergo exploratory surgery to discover the full damage caused.
A scan has revealed that Shane did, as was thought, dislocate his shoulder, before it immediately moved back into place," said Wales physiotherapist Mark Davies.
"He will now undergo exploratory surgery in the next 48hrs to assess the full extent of the damage caused by the dislocation, but we know he will be out of action now for a minimum of 10 weeks."
The Ospreys currently sit in second in Pool 3 of the Heineken Cup, just a point behind double European Champions Munster and will line-up against London Irish in back-to-back fixtures in December.