Few questions I'm afraid - how many leaves has it lost, just one or two or quite a lot? How long have you had the plant? how tall is it, and how big is the pot in terms of height from top to bottom (can't tell from your photo)

A few more
Has it ever dried out, has the pot a drainage hole, is it in full sun (chance would be fine thing this year)
Did you buy it in this pot, & when?
And could it have vine weevil?

I find it hard to grow, my garden isn't sheltered enough from the wind and sun.....
Is it in a sheltered area?

What part of the U.S. are you in, Lleeds? Areas with hot summers, like mine, severely stress Japanese Maples, especially the cut-leaf varieties.