Here is a wide angle pic of the tree..

The white spots on the trunk are supposed to be there. My michelia alba has those too. The drooping leaves indicate heat stress. Is it in full sun? Have you been watering it? My michelia likes morning sun and afternoon shade. It doesn't like being in full sun all day. Also, it likes lots of water during hot weather.

Thanks for responding. Our Michelia Alba usually receives full sun in the afternoon during the hottest part of the day.

It was looking a bit jaded about 2 weeks ago and I noticed the surrounding ferns had started to block its access to the sun. I cut the ferns back just before 2-3 days of scorching temperatures so quite possibly heat stress is the cause. We do water regularly but perhaps not enough given recent weather. I also noticed several whiteflies in the vicinity so insects may have contributed to the damage.

It definitely looks fried from the sun. So sorry!
Hopefully by moving it to a shady spot it will recover and put out new leaves.

Have you looked at the FAQ section?
They have lots of good tips for michelia.

"Michelia's light requirements are somewhat complex: as much as they like lots of light and warmth, full sun-even at the coast-dries out their leaves and turns them an unpleasant yellowish green. The ideal situation is direct morning sun followed by light dappled shade under high trees. This can translate into any one or a combination of these scenarios:
light all-day shade; full sun until late morning with part shade the remainder of the day inland; full sun until early afternoon, then part-shade the rest of the day near the coast. Strong afternoon sun in summer-even at the coast, is not a good situation for michelias."

Here is a link that might be useful: Michelia tips from the FAQ section