It's very unusual for a ficus to lose newer as opposed to older leaves. The most common causes of leaf shedding in tropical ficus are root congestion, low fertility, over/under-watering, soil compaction, a high level of dissolved solids (salts) in the soil/ soil solution, a marked change in light intensity or duration of exposure, sudden chill. Infection by fungal/ bacterial pathogens can also cause shedding, but your tree isn't presenting in any way that should lead you to think a disease is in play. The list doesn't help much because all the above cause shedding of older foliage.
Does the pot have a drain hole?
Does your home have an ionic exchange water softener (uses salt as the exchange medium?
How do you tell when it's time to water?
Al
