Lynn said he saw Rzepczynski rub at his eye immediately before falling to his knees.
"At first, he was swiping like he had something that had gone in his eye," Lynn said. "Then I saw some blood above his eye. I don't think it was the ball that hit him. I think it was mulch or an acorn or something like that. I wasn't close enough to see what it was or what happened, but I'm pretty positive that it wasn't the ball."
Choate said he didn't see Rzepczynski take the swing, but grew concerned when he went up to the left-hander and saw blood.
"He was just saying that it was kind of stinging and burning," Choate said. "He asked me how bad it was. It was just really red. The inner half was just really red."
Choate immediately drove Rzepczynski to the Cardinals' Spring Training complex so a trainer could evaluate him. Rzepczynski was then sent to a local eye doctor, who is scheduled to have a followup visit with Rzepczynski on Monday.
"It was serious enough that you knew he had to get him in here," Choate said. "The whole way up here he kept saying, 'Only me. This only happens to me. Only to Rzep. Only to Rzep.'"
Choate said he spoke with Rzepczynski later in the day and was told that there was no damage to the retina. Rzepczynski described his eye as "bruised" during that conversation and said that his vision was returning.
Manager Mike Matheny said he had no additional information to provide regarding Rzepczynski's current status on Saturday, aside from the expectation that "he's going to be laid up for a while." The Cardinals hope to learn more about Rzepczynski's prognosis after Monday's checkup.
Rzepczynski last pitched on Thursday, following a week-long layoff he had due to left biceps soreness. He was scheduled to return to the mound Saturday. Now that Rzepczynski is sidelined indefinitely, the Cardinals have to consider the possibility that the lefty won't be ready at the start of the season.
"We're just still at a point right now where we're hoping that everything clears up and that it checks out OK," Matheny said. "You can't get work [in] if he's in bed, so, yeah, that's definitely not helping him get ready for the season."
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.