I can't see any problem in the photo?
You have given no info on how you keep and water this so hard to pin down a single reason, only possibilities for you to consider.
Several reasons ficus could lose leaves:
1. old leaves will die and fall. Perfectly natural
2. lack of light. What seems good light to us is very dim to a tree
3. too little water. tree will drop leaves in order to stay alive until next rain (or, in the case of potted tree, watering). water well to completely saturate the soil but then let it get almost dry before watering again.
4. too much water. roots begin to rot if kept saturated for long period then tree cannot take up water and begin to die. let soil get almost dry before adding more water but then water thoroughly to completely wet the whole root mass.