With Francisco Liriano officially signing with the Pirates yesterday, details about his mysterious "non-pitching arm" injury were bound to emerge and today we have some thanks to Bill Brink at the PG, via El Caribe, a Dominican newspaper. The report is that Liriano broke his humerus by falling in his bathroom and that his arm was in a cast after the injury. Falling in the bathroom is one of those weird things that's hard to gauge. It definitely sounds like it could be a cover story for something else, but I could also see myself leaving, say, a beer fermenting bucket sitting out in the bathroom and tripping and falling over it in the middle of the night.
In any case, let's talk about a broken humerus in the non-throwing arm. Unfortunately, arm bones are not discussed in "Dry Bones," so instead click on over to Wikipedia and look at a humerus. We are almost entire bereft of other details here (whether it's a displaced fracture or not, whether there was a dislocation of the shoulder, etc.) so it's pretty hard to speculate on how long this sort of thing might keep him out, but let's look at his throwing motion anyway, because it's late January and these are things fans do in late January.
That's just for a point of reference and not any comment on Liriano's actual mechanics. The upper arm/shoulder on the non-throwing arm is what helps create the whipping motion that generates torque through the zone. Imagine pitching with a fracture in that part of the arm. There might be enough separation between the injury (which we know happened around Christmas) and when the season starts for him to get some innings in spring training and to be ready for April, but it's impossible to say that without knowing all of the details here. The same can be said for the Pirates' caution: it's possible to read into it a bit and conclude that the Pirates know the injury is serious enough to make Liriano miss time and that's why they wanted to renegotiate, but it's also possible that they simply want their bases covered in the event that Liriano misses a lot of time, no matter what the initial diagnosis is.