While this could simply be a strain of the triceps, it would not surprise me at all if this was a rotator cuff issue instead. This reminds me of a time my Doctor told me, "Well, Joel, it's likely indigestion...but it could be colon cancer." I know it's all in good fun, but he actually provides a nice follow-up, as opposed to leaving it at some random speculation: "Sheets will likely be evaluated and an MRI should be taken shortly. While this could simply be a strain of the triceps, it would not surprise me at all if this was a rotator cuff issue instead. The reason being, the triceps crosses part of the rotator cuff in the posterior aspect of the shoulder in what is called the "Quadrangular Space." The inner (long head) aspect of the triceps actually crosses over one of the rotator cuff muscles (teres major), and passes underneath another rotator cuff muscle - the teres minor. In between this intersection lies the axillary nerve, which, when compressed, can offer symptoms mimicking "stiffness" or "numbness" in the area of the triceps and posterior-lateral shoulder. In my clinical experience, I have seen very few baseball pitchers present with a pure, isolated "triceps strain" - rather, there is almost always an involvement of these rotator cuff muscles. A strained triceps certainly sounds better to the press than does a rotator cuff injury! If a DL stint is required, expect it to last the minimum 2 weeks, followed by a rehab start or two." Hardly just a worst-case scenario projection. I know Ben mentioned he was concerned, since the area in which he felt the soreness was near the latissimus dorsi muscle he tore on the back of his shoulder. From reading Chris's writeup on how the triceps 'underlaps' the rotator cuff, it sounds plausible that there could be something bigger here. However, I agree with the 'wait-&-see' approach.