Still, the loss of Chen for any extended amount of time would be a serious blow to the Orioles. Until Gonzalez returns, the O's three remaining starters are Jason Hammel, Chris Tillman (who starts today), and Freddy Garcia (who will apparently start tomorrow). Thankfully, the O's had an off day yesterday and have another on Thursday, but after that they don't have one until June 3. So they can juggle their rotation in the short term, but Chen's absence will matter soon, especially since his temporary replacement(s) will likely be some combination of Zach Britton, Steve Johnson, and Jair Jurrjens. Jake Arrieta is dealing with a shoulder strain, and Kevin Gausman doesn't seem like an option just yet. But anything's possible.
It's only May, but Chen has been the O's best starter so far. He put up an fWAR of 2.2 last season, but he's already up to 1.2 fWAR in 2013. His strikeouts have been down (from 7.19 K/9 to 5.13), but he's been walking slightly fewer batters while doing a much better job of keeping the ball in the ballpark (from 1.35 HR/9 to 0.57). But that's in only 47.1 innings, so who knows if that trend will continue, especially now that he'll have to work his way back from an injury.
Last season, Chen didn't have amazing numbers (4.02 ERA/4.42 FIP/4.34 xFIP), but he threw 74.2 more innings (192.2) than the team's next closest starter, Hammel (with 118). Tillman only pitched 86 innings, and although he's shown tremendous strides these past two seasons, he's far from a reliable option and even dealt with his own injury concern just last September.
Garcia is a wild card, and anything the Orioles get from him is a bonus. He wasn't as bad as his 5.20 ERA in 107.1 innings with the Yankees last season indicated, but he wasn't good, either. But there's a big difference between asking him to be a fifth starter type and being someone the team actually needs to pitch well for a couple weeks. He's been pretty lucky in 12.2 innings (.135 BABIP) and has been OK, but more of those balls in play will turn into hits, and since he's not striking anyone out, that's going to be a problem.
And then there's Hammel, who has not looked anything like the pitcher Orioles fans watched last season. His walks are up, his strikeouts are down, he's not getting as many groundballs, he's giving up more home runs, and his velocity is down. I'd say those are reasons to be worried. More than any other pitcher, the O's will need Hammel to step up in Chen's absence. It would certainly be helpful if the guy who put up 2.6 fWAR in just 118 innings quickly turned things around.
Maybe some of that Dan Duquette magic will present itself yet again, and Garcia and Jurrjens (or someone else) will shut things down while Chen recovers. It's unlikely -- but not impossible. Just look at what Vernon Wells, Lyle Overbay, and Travis Hafner are doing for the Yankees. But I'm not expecting great things, which will probably mean more innings for an already overworked bullpen. Get well soon, Chen.