Thrown correctly, no. However, it is in the heat of the game when the pitcher is trying to put just a little more on it when problems occur. I'd wait.
On the other side of the coin, have him develop a different curveball. For instance, not only having a 12-to-6, but turning just a little and throwing a 1-to-7 cureball. You still have the advantage of cushioning the arm on follow-through which you don't have with the slider.