"I knew it wasn't going to be perfect right away, and I knew I was going to have to deal with stuff this year, and I have," Jay said before the Cardinals opened a four-game series against the Padres at Busch Stadium. "But it just got to the point where we've got to take another step back."
Jay hit .248 in 30 games to start the year before he was placed on the DL in May. He has hit just .185 in 27 games since coming back.
The club initially thought Jay could be fully recovered from the surgery as early as Spring Training, and he began the season as the starting center fielder.
"I think he's really felt like it's affecting his performance at the plate," general manager John Mozeliak said. "I spoke with our medical staff and they really felt like the best thing for him to do is give it some time. When you think about the timing of this DL coupled with the All-Star break, it just makes sense."
Jay declined to get specific about discomfort the injury causes, other than to say it's "a little bit of everything." But manager Mike Matheny said it's a matter of Jay regaining the necessary strength to finish swings.
"I don't know the degree of what they're expecting or how much time [it will keep him out]," Matheny said. "But it seems whatever time we can give him will be a benefit at this point."
The injury comes at a time when another St. Louis outfielder is on the DL, as Matt Holliday is working back from a strained right quad.
The Cardinals remain hopeful Holliday could return from the DL before the All-Star break.
"I think he's progressing," Mozeliak said. "I do know he plans to make this [upcoming road] trip, so if you're making the trip, that means you're certainly getting closer. He'll work with our medical staff to keep pushing."
With Jay and Holliday out, Matheny said Xavier Scruggs and Mark Reynolds could be tabbed for reserve corner outfield duty and added that utility player Pete Kozma has been working in the outfield every day.
David Cobb is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.