be doubtful

References in classic literature ?
Who began it, or how fair it was, or how unfair, may be doubtful; but how it ended, is certainly not doubtful, for the victim was found throttled."
He's feeling a bit better at the moment but if the game was today he'd be doubtful."
"He would have to get some training in before the weekend if he was to have a chance so I would say he will be doubtful for Saturday."
ENGLAND midfielder Owen Hargreaves could be doubtful for the crunch World Cup clash with Nigeria on Wednesday after picking up a leg injury - courtesy of Michael Owen.