You would probably need to supply a little more information for the members here to help you. Pictures are always helpful. If that isn't possible then you could start by telling us what kind of maple. The approximate size, age of this and the others trees. I am guessing all the maples are the same??. The location of the dying tree relevant to the 'good' trees. Did the tree leaf out this spring and then lose its leave. Also a little about your micro climate. Are you near the shoreline 10 miles inland? Does the tree have any damage? We just need more info to even make a guess. 90% leaf loss is obviously not good but you never know.