Saints physio Jim Joyce said: "It is very disappointing for the lad because he has had a rough time this season.
"It is difficult to say exactly how long he will be out until after the operation but the last two players to have similar operations - Mark Draper and Luke Byles - were both out of training for four weeks.
"We are hoping Marian will just need a clean-out but the surgeon won't really know until he gets in there.
"The problem seems to be some scar tissue at the back of the ankle joint but it does not show up well on the scan so we need to go in and have a look."