well, even a healthy tree will lose leaves naturally and some of those about to be lost may turn yellow so not necessarily indicative of any significant problem. OTOH, if you are suddenly losing lots of leaves and/or the green leaves are looking pale you might consider a LIGHT application of a complete fertilizer. the other thing to potentially consider is drainage and/or overwatering---many "tropicals" actually appreciate a period of relative rest where they do not need lots of water and unless the growing area is warm all year may not need so much water at this time of year. there is also the possibility that the plant may be outgrowing the space in it's pot and may now have more roots than soil and so MAY appreciate being planted in a new larger pot with fresh potting soil. you can check by probing with your finger or a fork and see if there are lots of roots very close to the soil surface---if there is it may be time to consider a new larger pot.
hope this is of some help. good luck.