I take it loading of the axial skeleton in compression is what's causing you problems? The belt squat, along with continuing the leg press, will help maintain some of your squat strength. You might also be able to do lunges holding weights in your hands, or maybe even the much maligned Bulgarian Split Squat, both which you can find out by trying, conservatively.
Impossible to say exactly how much squat strength you'll keep, but it will probably be more if you do these things than if you don't.