A decision on Westbrook's status for Monday could be determined as early as Thursday night, Mozeliak said. Westbrook, through a team spokesman, declined to address the injury in further detail.
"Clearly," Mozeliak said, "right now from a physical standpoint, we're hoping he can work through it."
Even if the back stiffness were to subside, it is not a given that Westbrook will start as scheduled. He has been inconsistent since coming off the disabled list in mid-June after a bout of right elbow inflammation, and the results over the past month have been especially troublesome for a team in the thick of a division race.
Westbrook is winless in his last five outings, and he has allowed 38 hits, 28 earned runs and 16 walks in those 26 innings. Opponents have hit .345 off him during that span, with three homers. Westbrook has struck out only 11.
"Obviously, if you're dealing with something physical, that has to be addressed first and foremost," Mozeliak said. "I think the performance as it stands in its own silo, you look at in terms of we need to try to put our best five [starters] out there, if possible. I do think from a medical standpoint, Westy is dealing with something. Now we have to determine what's the next best step for him."
As the Cardinals' rotation order stands now, Westbrook's next three starts would come against the Reds at home, the Pirates on the road and the Pirates back at Busch Stadium. The fact that all three would be against the two teams the Cardinals are trying to beat in the National League Central augments the necessity of sending out the starter they feel gives them the best chance to win.
Even when healthy, Westbrook has fared poorly against the Pirates throughout his career. In 15 games (11 starts) against Pittsburgh, Westbrook is 1-8 with a 4.98 ERA.
If Westbrook can't start on Monday, the Cardinals will pick a starter from a group that includes Michael Wacha, Tyler Lyons and Carlos Martinez. The spot starter is likely to be determined, in part, by how manager Mike Matheny has to use his bullpen between now and then. Both Wacha and Lyons are currently in that seven-man 'pen. Martinez is scheduled to start for Triple-A Memphis on Friday.
Finding help externally seems a long shot with the August waiver period nearly over. A dearth of players passing through waivers, the process of not being able to claim a player on waivers until every team with a worse record passes, and the asking prices for those players made available, Mozeliak said, have all limited the outside options.