Hi Brian,

You can find cement repair compound in your local home improvement store, or use normal cement. Definitely repair the crack before doing the tile. If the crack grows wider (even after repairing) it will crack your tile in the future.

Its why when we see this, we often recommend a floating floor in this problem area.

Be sure to first chip away unstable edges then use a wire brush and Shop Vac to clean out all the debris from the crack. Once you're down to stable concrete you can apply the concrete patch material.