You could say it has to do with either the potential lying of his age, his wrist injury. It could be anything. I'm not saying steroids is out of the question. With so many stars having been caught, it basically means no one is excluded from this scandal.
If he didn't do them, I'd say this slump is a product of his age or his injury...the loss of his timing.
However, it isn't far fetched to believe he has done them in the past. The look of the trading card, his physique has changed over time. I mean, he could have started eating more, trained to gain some weight, but who knows.
If he has done steroids, that would explain his gain, and also could explain his injury. If his wrist muscles sliced through his wrist tendons, that could definitely be a sign of steroid use. Tendons weaken when steroids are used, only muscles get stronger.
Not saying this is what has happened, but it is a possibility. He could've used them, is off now because so many stars have been caught, and his real ability is starting to show.