He experienced spasms during Sunday's first inning, and an ill-advised jump throw on a fielding play in the third (for an error) didn't help. Chatwood, who entered with a 1.30 road ERA, gave up six runs (four earned) and six hits, and walked five, in four-plus innings.
Head athletic trainer Keith Dugger visited the mound, and Chatwood threw an allotted warmup pitch to test his health, during the fifth, but the back didn't improve.
Chatwood admitted it "wasn't the smartest idea," but he felt he needed to pitch in pain to help a tired bullpen. The Rockies received short starts in the previous three games, all played in stifling heat and humidity -- five innings from Chad Bettis in a 12-9 victory at Texas on Thursday, four-plus from Jon Gray in a 10-6 loss Friday and three from Tyler Anderson on Saturday, before he was ejected from the 6-3 loss.
But the pain severely limited Chatwood (10-8), whose fastball movement keys successful performances.
"I stayed arm side the whole game. I couldn't get to my glove side, and I couldn't finish breaking balls," Chatwood said. "So it's tough when you're pitching fastballs to one side of the plate."
If Chatwood can't make the next start, it isn't clear how the Rockies will cover.
Right-hander Jeff Hoffman, the Rockies' No. 3 prospect according to MLBPipeline.com and a key figure in last year's trade that sent star shortstop Troy Tulowitzki to the Blue Jays, threw five scoreless innings, with one hit and nine strikeouts on Sunday for Triple-A Albuquerque at Colorado Springs. The Rockies would have to clear a spot on the 40-man Major League roster if Hoffman was called upon.
Another option is right-hander Eddie Butler, a former first-round pick who has been with the Rockies for parts of the last three seasons. Having adjusted his delivery, Butler has shined in his last two starts in Triple-A, allowing just two runs over 15 combined innings.
Butler is scheduled to pitch for Albuquerque on Monday, but the Rockies' off-day on Thursday would make it easier to fit Butler into the rotation, and he is on the 40-man roster.
Long reliever Chris Rusin, who threw three scoreless innings when Anderson was ejected Saturday, is an in-house possibility.