Water, water and more water, at least a gallon a day, although you haven't said how big the plant is.

Most recent shrub/tree transplants need plenty of water to sustain them while they recover and to encourage new root growth.
Don't worry if you lose most of the leaves as new leaves will open when the roots regrow.

Bamboo and Stjohntongue - Many thanks. It is quite a tall specimen but with all the rain in the past two days I hope it will perk up.

Well unless its coming down in stair rods all day long, I'd be out there with a watering can or bucket and chucking it at the roots anyway.

Here, here, bamboo.