Gavin Floyd is a frustrating guy to have play for your favorite team.
Floyd is frequently dominant for stretches. He's 4-1 with a 1.37 ERA in his last four starts, and he had a 2.53 ERA over his first 46 1/3 innings of this season. Floyd can also be awful for extended periods. A good example would be a six-start stretch from mid-May to mid-June where he was rocked for 35 earned runs in 30 1/3 innings.
What Floyd's bipolarity generally amounts to is a pretty good pitcher. His numbers this season (7-8 record, 4.54 ERA, 91-31 K-BB ratio, 4.61 FIP) are pedestrian, but Floyd posted WAR totals, per Fangraphs, of 4.5, 4.3 and 3.6 during the last three seasons, ranking 16th in baseball in pitching WAR during that time.
Floyd may not be Justin Verlander, but he's also valuable enough for his team to feel his absence in a tight pennant race. And unless they can pull another Jose Quintana-esque rabbit out of their hat, the White Sox could really be hurt by Floyd's absence.
John Danks remains disabled, and Phillip Humber was hurt, though he's being activated to take Floyd's place in the rotation, which is turning into a problem area. Chris Sale and Jake Peavy are still there, of course. They've been awesome, but neither is exactly a lock to stay off the DL for 11 more weeks. Humber has a 6.01 ERA and is walking 4.14 batters per nine innings this season. Beyond those three are unproven call-ups, and not ones that were highly touted entering the year. Quintana has been fantastic, and Dylan Axelrod has not, but counting on either for too much is a bad idea.
With the AL Central's sleeping giant, Detroit (which has won eight of nine), finally making its long-awaited move and Chicago's division lead at 2 1/2 games, now isn't a great time for the Sox to sputter. The status of their rotation is only going to make holding off the Tigers more difficult that it would be otherwise.