Bristol City were fined £200.000 by Liverpool for not giving Kent enough playing time.

Chelsea wouldn't be the ones pissing him off, it'd be a league rule.

As for it being unreasonable, that'd be entirely subjective depending upon a number of factors, but the player could absolutely refuse to go on loan, he'd just not be able to play anything but U23s football. The link you provided mentions financial reasons, or moving abroad, neither of which would apply.