"It just didn't feel like I would have liked for it to," Westbrook said. "It's not comfortable. It's definitely not where I want to be. But we'll figure out another course of action."
Westbrook had been methodically building his arm back up after a cortisone shot was administered on Thursday to help break up scar tissue around his elbow. He resumed throwing on flat ground on Sunday, repeated that work on Monday and Tuesday, and had hoped that Wednesday would put him a step closer to returning to the St. Louis rotation, potentially as early as next week.
But Westbrook said he could feel almost immediately that something was not right with his arm. He continued throwing to see if the discomfort would go away before determining that he needed to stop.
On a day that the Cardinals learned that Jaime Garcia would need season-ending surgery, this setback in Westbrook's throwing program throws the rotation into additional flux.
Matheny declined to say whether the organization is considering a change of course with how it plans to fill these open spots in the rotation. Options include summoning pitching prospect Michael Wacha or sending someone out of the current bullpen -- namely Joe Kelly or Carlos Martinez -- to begin building back up as a starter.
"We have to watch and see what happens," Matheny said. "It's hard to say right now."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.