Siegrist retired all four batters he faced on Friday, but notified the training staff afterward that he could not get loose during the 11-pitch appearance.
"It got to the point last night where he felt like it was not improving," Mozeliak said. "It's not acute. It's just something where he feels like he just can't get loose. And so when he's throwing, it's not that he can't throw or is in extreme pain. It's just sort of a mild discomfort."
Before Friday, Siegrist had pitched just once in an eight-day period. On several of those days, he was designated as available only in an emergency situation. The Cardinals had hoped that rest would alleviate this issue. Manager Mike Matheny said that Siegrist passed several tests and was cleared for usage on Friday, which is why he was deployed in the seventh inning.
Siegrist had been one of the most heavily used relievers in the Cardinals' bullpen before this recent layoff. He appeared in half of the team's first 44 games, logging 18 2/3 innings during that stretch. Mozeliak downplayed the possibility that this injury could be related to that workload.
"Certainly, when he's feeling better again, we'll have to watch his usage moving forward," Mozeliak said. "But I don't feel like you could conclude there was a usage factor."
Left-hander Sam Freeman was recalled from Memphis to take Siegrist's place in the bullpen. He was expected to arrive at Great American Ball Park around game time Saturday.
Freeman was optioned to Triple-A only a week ago when the Cardinals made room for Jason Motte. Freeman made one scoreless appearance for the Cardinals. Typically players have to remain in the Minors for at least 10 days after a demotion, though that is waived in cases where a team makes a DL move.
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.