Prince Frederic von Anhalt tells TMZ ... he has to decide whether to allow doctors to operate on his wife's leg -- which was badly infected because of a blood clot.
The docs have said putting the 93-year-old Zsa Zsa under anesthesia and operating is "very risky" ... the doctors say there's less than a 50% chance she'd survive the procedure.
The Prince says the other option is continuing the antibiotics for the next 3 months. The problem there -- the medication could destroy her kidneys.
Von Anhalt says he hasn't decided what to do, but he feels the pressure because a decision must be made by tomorrow AM.