From descriptions of the animal, it is unclear if it is a feral domestic or a larger species brought to Detroit as a pet that escaped or was released, the Detroit Free Press reported.
One witness said the cat was 4 feet high, although others described a smaller animal. The Maine Coon cat, one of the largest domestic breeds, stands less than 2 feet tall although some of the larger ones measure 4 feet from the head to the tip of the tail.
Paul Hatley, 14, spotted the cat a few days ago.
"It wasn't normal," he said. "It didn't run away like normal cat. It just stared at you. ... It was scary."
Nathan McGuire, who described the cat as being 4 feet high, has also taken the only known picture of the beast. It shows a gray cat with black marking.
Domestic cats are believed to have been bred from African wildcats thousands of years ago. While the African wildcats are roughly the same size as house cats, their cousin, the European wildcat, is larger.