Penny acknowledged that he first felt discomfort in the area after his previous start, five days earlier in Cincinnati, but did not report it to the team's training staff. He threw a bullpen session in between starts, feeling the injury "a little bit," before taking the mound on Friday.
"I didn't feel it when I was pitching [against the Reds]," he said. "The day after, I felt a little stiff in there. ... I knew it wasn't my shoulder or my arm or anything. It was just kind of annoying. I could feel it when I reached back for something. I was hoping that it wouldn't be a problem, but obviously it was a little worse than I thought."
General manager John Mozeliak confirmed on Friday night that right-hander P.J. Walters is on his way to St. Louis to join the team on Saturday afternoon. Mozeliak said that the club has not yet determined who will be placed on the disabled list to accommodate Walters.
The options are Penny and reliever Blake Hawksworth, who is sidelined due to a sore right groin. The club will determine which player will be shelved on Saturday morning after further evaluation of the two injured players' situation. It is also entirely possible that one pitcher will be placed on the DL on Saturday, and a second move will follow it in the ensuing days.
Saturday would be Walters' day to pitch for Triple-A Memphis, which is playing at Sacramento this weekend. So he will be available to pitch multiple innings in relief over the weekend. Any decisions beyond that remain a bit hazy. Walters could take Penny's next turn in the rotation, or the Cardinals could look to Adam Ottavino to take that job.
"I don't know yet," Mozeliak said when asked about Walters' role going forward. "We'll see. But obviously he'll cover innings tomorrow."
Penny's removal from the game capped a highly unusual sequence that began with him hitting a grand slam in the bottom of the third inning. Facing the man he replaced in the Cardinals' rotation, Joel Pineiro, Penny cranked a tie-breaking, two-out slam after the Halos walked Skip Schumaker intentionally with two men on. Penny took a curtain call after the blast, and he took the mound as normal in the top of the fourth.
After taking his warmup throws, though, Penny stopped and convened a conference at the mound. With assistant athletic trainer Greg Hauck among those checking him out, Penny was immediately removed, and Mitchell Boggs was brought in to relieve.
"Right away, 'Dunc' [pitching coach Dave Duncan] saw it and brought my attention to it," manager Tony La Russa said. "In fact, he was yelling to him, 'Don't throw anymore.'"
Penny said that he did not aggravate the injury on his swing, and that in fact it doesn't bother him when he swings. He pointed instead to the long inning that his homer contributed to, noting that he had an extended period of time between pitches thanks to the five-run outburst.
The injury may also complicate matters for reliever Hawksworth, who is considered unavailable for the weekend due to a right groin strain. With the Cards asking for six innings from their bullpen on Friday, and Hawksworth out until at least Tuesday, it could make sense for St. Louis to go ahead and put Hawksworth on the DL and call up a reliever to take his place.
Penny was the second Cardinals pitcher to hit a grand slam in less than eight months. Chris Carpenter hit one against the Reds at Great American Ball Park last October.
It was the third home run of Penny's career, and his first since 2003, when he was a member of the Marlins. Penny had never hit a grand slam before in the Major Leagues.
Penny has been outstanding on the young season, sporting a 3.23 ERA even after his abbreviated four-run showing on Friday.
"When a guy like Brad goes down, that's a punch in the gut, especially with the way he's been throwing the baseball," Boggs said. "He's as good as anybody in this league right now. We understand that that's a tough blow, but the type of team we have, we'll bounce back. Guys will be ready, guys will step up, and hopefully he'll be able to be back as quick as he can."