I'd keep an eye on things initially, but if it appears your cat doesn't show any tendencies to attack chickens, I wouldn't worry in the least. I'm MUCH more leery of dogs around a flock, as it seems their instincts (unless trained) are to kill as many as possible simply for sport.

Sickening.
From someone who's owned numerous kitties in her life, they normally prefer smaller, easier prey, such as mice, moles, and songbirds. Full-sized chickens are rarely threatened, unless of course we're involving a starving feral. Even then, it's not likely. Chicks could technically be an attainable target, although mine refuse to touch even the smallest of Old English Game bantam babies. These little fireballs don't "act" like prey animals, being that they'll stand up to a cat rather than flee. Flight activactes a feline's predatory inclinations.
Let's just say, not only do my well-fed house and barn cats leave our birds (including many bantams and chicks) be, but ferals, strays, and neighbor's kitties haven't made any attempts. I suppose it's not out of the realm of possibility, which is why I recommend supervising to avoid preventable issues, but doubtful.
~Alex