One of my Acers has no leaves at all - the buds looks dry. I have been watching it for a few weeks now and took action a few days ago as the buds have not produced leaves yet whilst its twin has. I took it out its pot and found it was very dry and pot bound (even though I repotted in Autumn and have been keeping it watered). It is now in a larger pot with fresh soil and feed. Perhaps you can check that your Acer is not too dry and shift it to shady spot?

Thank you kindly for your advice Kildermore - unfortunately my Acer is actually a 15-foot tree planted in the ground! But thank you very much for your interest and I do hope that your Acer recovers well.