I've noted this in a couple places (and in this blog before) but the Nats have been incredibly lucky when it comes to starter health. In 2012 their starters basically missed no starts because of injury. Strasburg missed a few because he was shutdown and Detwiler didn't pitch a full season because Mike Rizzo wanted to prove how smart he was re-signing Chien Ming-Wang, but while in the rotation they pitched every time out. 2013 wasn't quite as remarkable but they were still pretty healthy. Detwiler missed most of the season as #5, but Strasburg & Haren both only missed a couple of June starts.
Overall that means for the Nats Top 4 starters in 2012 and 2013, they started something like 246 of 250 possible starts. (something like that)
Of course this season, Fister already blew that out of the water missing his first 6 or so starts. Now Gio will miss at least one (I'd bet two). With the Nats fighting to stay near the top of the NL East, with big bats out of their lineup, this is a loss they can't afford. That's why the cleared MRI makes you feel a little better. One or two missed starts? Ok, you might throw in a Treinen or Jordan (looks like Treinen right now) and get a lucky couple starts. But in the long run it's going to cost you.
How much will it cost? Hard to say but Gio was (roughly) the 13th most valuable pitcher over the last couple of years. (Looking at fWAR to get an idea). More valuable than Strasburg (mainly because Strasburg pitched 50 fewer innings), more valuable than ZNN. The latter might not seem right to the brigade of people who have made ZNN the Nats bestest starter in their head, but Gio's 2012 was a good deal better than ZNN's despite having similar ERAs (2.89 for Gio, 2.94 for ZNN) which puts him over the top.
We can look at that a little deeper :
Gio 2012 : 207 Ks, 1.129 WHIP, 9 HRs
ZNN 2012 : 153 Ks, 1.170 WHIP, 18 HRs
Both have very good stats, butwhat makes Gio's 2012 noticeably better is in the details. Gio had much better numbers in two of the three things all on the pitcher (HRs and Ks). ZNN did have much better numbers in the third thing (BBs) but that matters mostly in terms of putting runners on base. ZNN managed to keep guys off the basepaths by not walking them (2.0 BB/9 to Gio's 3.4) but Gio did the same by not giving up hits (6.7 H/9 to ZNN's 8.6). You don't need fancy stats to tell you you'd rather have a guy give up two walks in an inning than two hits. Overall Gio was at least a step better than ZNN in 2012, so despite ZNN being a little better than Gio in 2013 (people seem to forget ZNNs 2nd half slide back from awesomeness) take the two years together and Gio's been the most valuable.
If you are looking for a silver lining, the pitcher who was 14th in fWAR the past 2 years was Doug Fister. So the Nats aren't losing a step with Fister coming in and Gio going out. Of course the problem was the Nats wanted to pick up the pace - not maintain it.
Strasburg vs Cueto is not happening. The Reds threw in Tony Cigrani YESTERDAY for reasons I can't quite understand. (why press him to come back in Citizens Bank park where a mistake is a HR?) but anyway it pushes their rotation down. Strasburg vs Leake, Cueto vs Fister, Simon vs Roark.
Personally I'd really like to see Strasburg WIN this game tonight. I've felt he's only done that once this year (2nd start of the year vs Marlins - Padres start might have been better but Nats had big lead by end of 3rd). With Votto out this offense should be dead. They've scored more than 4 runs once since May 3rd. They strike out more than any team in the NL but one.They don't hit the long ball particularly well. They DO walk but the pitcher, especially one like Strasburg who has good control, can cover that. All the pieces are there for a gem. Make it happen.