Step 1: Check the square root condition.
For the expression
\[
\sqrt{4-x^2}
\]
to be real, we need
\[
4-x^2 \geq 0
\]
So,
\[
x^2 \leq 4
\]
Hence,
\[
-2 \leq x \leq 2
\]
Step 2: Check the logarithm condition.
For
\[
\log\left(\frac{\sqrt{4-x^2}}{1-x}\right)
\]
to be defined, the argument of logarithm must be positive.
Therefore,
\[
\frac{\sqrt{4-x^2}}{1-x}\gt 0
\]
Step 3: Analyze the numerator.
Since
\[
\sqrt{4-x^2}\geq 0
\]
For the fraction to be strictly positive, the numerator must be positive.
So,
\[
\sqrt{4-x^2}\gt 0
\]
This gives
\[
4-x^2\gt 0
\]
Hence,
\[
-2\lt x\lt 2
\]
Step 4: Analyze the denominator.
The denominator is
\[
1-x
\]
For the fraction to be positive, and since the numerator is positive, we need
\[
1-x\gt 0
\]
Thus,
\[
x\lt 1
\]
Step 5: Find the common interval.
From Step 3,
\[
-2\lt x\lt 2
\]
From Step 4,
\[
x\lt 1
\]
Taking the intersection, we get
\[
-2\lt x\lt 1
\]
Therefore, the domain is
\[
(-2,1)
\]
Step 6: Final conclusion.
Hence,
\[
\boxed{(-2,1)}
\]