In a recent article on this site I showed that CC Sabathia has thrown fewer sliders than last year so far this season, especially in his past three starts. I wondered if this was because of an injury. The article has received some attention, and recently on Baseball Prospectus, Will Carroll wrote about Sabathia, disspelling any notion that he's avoiding throwing a slider due to an arm injury.
I do think it's significant that Sabathia has thrown fewer sliders, and there is a possibility that he's hurt. However, even if he is hurt, this is probably not the reason that Sabathia is avoiding his slider, as Carroll points out. We still don't know why Sabathia is throwing fewer sliders this year, but I should reiterate that four starts is a TINY sample size. It's quite likely that Sabathia's pitch selection is random (perhaps scouting reports against the teams he faced suggested fewer sliders), and it's quite possible that his poor performance is a result of him simply being in a funk.
As an Indians fan, Carroll's article was heartening. If Sabathia is indeed healthy, he should be able to right the ship soon. No one ever said pitching was easy.