When Jake Peavy went down on July 6th, 2010 with a season-ending shoulder injury, it didn't doom the White Sox playoff chances, it simply reduced their margin for error.
Similarly, John Danks being diagnosed with a Grade 1 subscapularis tear doesn't at all draw the curtains on the scuffling, yet division-leading 2012 White Sox, but it makes the already delicate dance Robin Ventura is trying to pull off with his pitching staff significantly harder.
The comparison might seem odd, since Peavy was a house of fire at the time he went down for a Sox team so hot they powered into 1st place at the All-Star break even in his absence. Looking back, it's unclear how Jake was doing it, rapidly improving his performance while his shoulder was fraying and deteriorating.
For this team, at this time, Danks does not exist as a productive starter, but as a concept for relief. His eventual return would allow for Humber, Floyd, and Quintana to battle in a meritocracy for their spots.
Part of the belief that Danks would step in and provide aid--other than that his contract situation guarantees him a slot--was the hope that his early-season struggles could be attributed to his shoulder problems. The good news is that it's more likely that they can be, the bad news is why.
To roughly summarize Mark Primiano's excellent summary of the injury, Danks is suffering from a fraying of primary muscle forming the rotator cuff. While the lack of a complete tear means he's a good bet to avoid surgery, shoulder injuries for pitchers are not known for their triviality, and pinning down the recovery time at this moment is a fruitless pursuit.
The very eager-to-return Danks has nothing to offer:
"I don't know any schedule at this point or anything. It’s frustrating because it feels good one day and then it feels like crap the next day."
Until there's more, no good refutation of Mark's grim assessment can be made:
"The bad news is that the way you likely avoid surgery with this injury is to shut him down for a long time. Like, maybe the rest of the season."
Danks need to rest and rest, and rest some more, and since his first comeback trial involved missing three weeks and experiencing more inflammation and soreness after a rehab start, estimations for how long it will be until his next one start there and extend farther.
In the mean time, the problems of Gavin Floyd and Philip Humber (one quality start between them in the last month) become a great deal more pressing, and Jose Quintana's continued success is a great deal more vital. Considering that Mark Gonzales' article on the topic listed Simon Castro as the foremost contingency plan--the 24 year-old return from the Carlos Quentin deal who's doing pretty much what Quintana was doing in AA before he got called up--the days of fantasizing about trading from starter depth to shore up the lineup seem distant.
If Danks, Quintana, Floyd, and Humber will all coin flips to be useful rotation members from here on out, the Sox lost the one throw they could afford to go against them. Since they're something more complicated than coin flips, and a healthy Danks was probably the best bet, the damage is a fair bit worse.
The lights certainly didn't go out on the Sox playoff hopes, but everyone will need to work harder to keep them on.