I guess, I'd keep an eye on it, if it keeps getting worse, maybe throw a shade cloth over the plant and get some kind of fungal treatment going, if new growth is clear it might be a chemical burn or still sun burn, but if the new growth is clear the shade cloth is not really necessary it may just be that the old leaves were not used to that kind of exposure and are going to respond to the sun like that - but it will grow out of that with the new leaves being happy and adjusted to that kind of sun level.
