unknown quantity (noun) dark horse: remote possibility
Sinonime: also-ran, hundred-to-one shot, improbability, little chance, little opportunity, long shot, outside chance, outside shot, poor bet, poor lookout, poor possibility, poor prognosis, poor prospect, sleeper, slim chance, small chance, stalking horse,
underdog, unexpected winner,
unknown, unknown quantity, unlikelihood, unlikely winner, upsetter