as King stated you really should check the roots for problems and worry more about that than the splitting leaf issue to start with a split looks bad but can heal at the point its is splitting and still survive just fine if roots can support it still....
Bad roots will mean intensive care for a while starting with unpotting it and a clean up then new medium.
does it by any chance have smaller new leaves in the center growing at the present or just the big mature leaves?
My guess is that it's most likely what King said, either a lack of proper humidity of a lack of adequate watering. How is the media in which the orchid is planted? If it's not in good condition then you should repot as soon as possible.