poor possibility

also-ran long shot sleeper underdog

hundred-to-one shot improbability little chance little opportunity outside chance outside shot poor bet poor lookout poor prognosis poor prospect slim chance small chance stalking horse unexpected winner unknown unknown quantity unlikelihood unlikely winner upsetter

chance in a million ghost of a chance impossible no chance no way not a prayer poor outlook poor prospect slim chance small chance snowball's chance in hell unthinkable very little chance when hell freezes over