When in good repair, a fitness ball in an effective piece of workout equipment. You can use it as a base for bodyweight exercises like push-ups and planks, or as a stand-in for a weight bench. But if your fitness ball starts leaking or shows obvious wear, it's no longer safe to use. Experts advise against trying to repair a leaking fitness ball. You're much better off simply replacing it.
The Potential Consequences
Although you might find a way to patch a fitness ball, that patch would become a lingering weak point. Given that most potential uses for a fitness ball have you positioned on top of the ball -- sometimes with weights poised overhead -- the risk is simply too great that your body weight, combined with the air pressure inside the ball, would cause a blowout.
The end result would be, at best, a quick and undignified trip to the ground, and, at worst, a serious injury. With brand-new fitness balls readily available for less than $20, repairing a leaky ball just isn't worth the risk.