The stress reaction at least is not a fracture. Just him pushing off too hard on his right foot when running the basepaths. With a special boot (just certain padding to help relieve discomfort), he'll be able to pitch, but as seen last night, he may not be able to go deep (6 will probably be his limit for the next two weeks).
Also he could give up a few more home runs, causing his ERA to rise a little, because he will not want to push off as hard on the foot.
My guess is that in two weeks, he'll be back to normal.