Vorm missed Monday's 1-1 draw with Hull City and the Dutch international, who is keen to feature for his country at next summer's World Cup, has admitted that he requires an operation to try to solve the issue.
The 30-year-old told reporters: "I have to do it now before the World Cup and we don't have too many league games in January.
"I have had some problems with my left knee for a while. It keeps swelling up, I have had some problems with it in the last few weeks and we have tried to manage it.
"We will try to manage it for a month and then at the beginning of January, I will have an operation. Then I will be out four weeks. This month, we have five or six games until the beginning of January."
Vorm has made the journey to Switzerland for Swansea's game with St Gallen, but it is unclear whether he will feature in their crucial Europa League clash.