I am betting you will be ok, but a question? How much mileage (long run) were you up to before the stress fx?
Definitely do what Coach Charles said, and stay active...elliptical (if you can tolerate it), deep water running, or bike.
I was developing one before I did Goofy in 2010, and it became symptomatic about 5 weeks before the race. I finally saw a doctor about 3 weeks out and got put in a boot. I did a LOT of deep water running (before and after seeing the doctor), all the way up until the race weekend. I also did a fair amount of time on the bike/trainer.
For race weekend, I had semi-clearance from the doctor to go ahead with the races, provided I would be SMART and stop if it got painful. I wore the boot all the time, except for when I was racing, just to keep my foot protected. During the races, I did a modified Gallowalk pattern of running 3 minutes ez and walking 2 minutes. Got through the 1/2 marathon ok. Was hurting starting around mile 22 of the full marathon, but by then, I was so close to my Goofy, I just finished it out.
Amazingly, even with the relatively large amount of walking I did, I finished the half in about 2:40 and the full in about 6:00.
Then stayed in the boot another 6 weeks to be sure. Because I knew that I probably set back the healing of the stress fx by doing the Goofy, but it was my informed choice and being prepared to deal with the consequences.