I have this on my leaves at the end of the season right before they shed in preparation for Winter. It seems to be the way they deteriate since from Spring until then they are the nicest solid green. I think they can get a rust disease like lots of other plants but why right before falling. Just be sure to collect the fallen leaves & discard properly. I wouldn't use the leaves as mulch either. Remember, next Spring your babies will put out all new leaves.

Thanks tabb! So no need to worry about a disease or viruses?

Figs are pretty much bulletproof. You only need to worry if the terminal bud (at the end of branches) turns brown during the main growing season.