I have a tree like that - squirrel planted, that I decided to keep. A post oak, I think. No fire problems, but I need to keep track of it so I can favor it when I work in that part of the yard. I spent a number of years fighting forest fires and observing how areas grow back after fires, so these remarks are based upon those observations (I studied forestry and botany in my undergraduate work, and these led me into forestry for a few years).
Depending on how hot the fire, if it didn't burn the roots, then chances are good it will come back next year. Grass fires are usually hot and fast, so chances are it didn't linger over the spot long enough to either super-heat and cook the tree roots or burn through to the cambium layer (under the bark). Scorching the leaves will make it look bad for now, but it isn't a death sentence.
The trick is to keep it alive until next spring, when you can really see what kind of condition it is in. In the wild, a tree would just stand there, no attention, with the scorched duff of the forest floor releasing newly freed nutrients into the ground every time it rains. Fires can be very good for trees. TLC, treating your tree by fertilizing or watering, is not going to be too effective if it doesn't have the leaves in place to help use those. It could make things worse by rotting the roots. I would suggest mark the spot, if necessary, so you can find it again (nothing like trimming or mowing something you wanted to keep), mulch lightly around it, and don't let it dry out completely if we have a really dry fall, but don't overwater it.
Sometimes they'll put out a new set of tiny leaves after something kills the first set. A fire in July may have been early enough that it would do this. I'd still treat it very gently, almost with benign neglect, and let it come back next spring. There may be some soil amendments you can add to the area without watering them in. How is that part of the yard or property normally cared for? What is this tree accustomed to as far as water, etc.? Take that into consideration.