$path = "L:\Lease Doc's\Track Lease Agreements\00770\/";
$that = preg_match('/[\\][0-9]{1,}[\\]/', $path, $matches);
print_r($matches);

PHP Warning:  preg_match(): Compilation failed: missing terminating ] for character class at offset 15 in F:\jobs\DirecetoryCheck.php on line 21