It's rough to tell from pic, but pic looks like finish has been removed. However your response says sanding, which would indicate a damage in the finish, but not in the wood.
Assuming the finish is damaged (is cloudy, milky whitish, etc.) I'd proceed in the following sequence until damage is repaired. Note, sometimes you have to try each step a couple times:
• Apply an oily substance, such as petroleum jelly or mayonnaise, to the damaged area and allow it to sit overnight. The oil will often force the water out of the finish. It may take a couple tries, but if no result go to next step
• Heat the finish with a hair blower set on a medium setting and don't stay in one place too long. The heat can cause moisture to evaporate. Avoid getting the finish any hotter than is comfortable to touch. It may take a couple tries, but if no result go to next step
• Dampen (not wet) a cloth with denatured alcohol and gently go over the damaged area using a motion like a plane coming in for a landing and then taking off again...it should leave the appearance of a comet’s tail of evaporating alcohol trailing as you wipe. (You can practice by wiping across a more resistant surface such as polyurethane or plastic laminate.)
• Cut through the damage by rubbing with a mild abrasive such as a very small amount of toothpaste or with salt mixed with olive oil. Rub the damaged area until the water damage is gone, being careful not to rub through the finish. Then, if the sheen is different from the surrounding area, even it by rubbing the entire surface with paste wax.
Let us know the results
Bob "Boardman" Borders