Leave it alone.
Opossums are cat sized marsupials.
Like the kangaroo, their young are born as embryos and make their way to a pouch on the stomach where they continue to develop. When they are four or five inches long they start leaving the pouch to ride on the mothers' back. When they have reached seven to eight inches body length, they leave the parent to make their own way in the world. Opossums are nocturnal, roaming at night, and looking for a dark, secluded place to sleep during the daylight hours. They are scavengers, and eat anything.