The latest issue is not a setback, Garza said, but a warning that he isn't ready to resume throwing.
"Now we know it's just time," Garza said. "We pushed it and pushed it hard. With the recovery rate I was on, everything felt great and we said, 'Let's go, let's go, let's go.' It's just the body's way of saying you still need to take a little more time.
"It's not a setback, it's more like coming to the realization that you can't out-mind your body too fast," he said. "It's fine. Yeah, I'm not on pace now to open up [the regular season], but I'm going to keep pushing and keep trying to get there."
Not having Garza or Scott Baker, who is recovering from Tommy John surgery, means Travis Wood and Carlos Villanueva are now in the rotation, joining Edwin Jackson and Scott Feldman. Sveum also officially named Jeff Samardzija as the Opening Day starter.
Garza had been projected to be ready for the start of the season after missing the last 2 1/2 months of 2012 because of elbow problems. His elbow has not been a problem this spring, but Garza felt some soreness in his lat halfway through a live batting practice session Feb. 17. He threw 20 pitches of 40 scheduled for that day, and then was shut down. On Thursday, he played catch for the first time since the Feb. 17 workout, and then did so again Saturday.
He felt some discomfort late in his workout Saturday.
"It didn't hurt, it's just not gone, and with stuff like this it has to be gone," Garza said. "If it's not gone, we have to get off the pedal. I'd rather keep pushing it down. Like I said before, I can't be selfish. It's still real early. If I can help my team out for 5 1/2 months, that's better than nothing."
Sveum had described Garza as being "pretty down" about the latest news, but the right-hander seemed to accept it well when he met with the media before Sunday's game.
Garza, who was 5-7 with a 3.91 ERA in 18 starts last season, will be a free agent after this year. He hasn't pitched since mid-July. Does he think about his contract status?
"I can't really think about that unless I get on a mound," Garza said. "I just want to pitch. Since I got back, I just want to pitch, I just want to go out and play and that'll take care of itself. Everything is going to take care of itself and I'm going to go out there and compete and help the club win games."
Lat injuries can linger, but Sveum said this isn't as serious as some which hurt when you sneeze or laugh.
"It's just to the point where he's just not ready to throw a baseball yet," Sveum said. "It's not torn or real bad. It's just not quite ready to throw. It's not a setback, it didn't get worse, it's just not ready -- it's like an evaluation process. Obviously, the evaluation was that he's not ready to step up any extra intensity throwing."
Having Wood and Villanueva as options certainly helps. The Cubs didn't have that kind of depth last year.
"That's the nice thing about the depth we bring in, to be able to fill those two spots," Sveum said. "We pretty much knew Baker would be the middle of April. We weren't quite sure how the elbow would respond from Garza and that was going really well. Now we have this minor setback that obviously could turn into missing two weeks to a possible month."
What's next for Garza?
"Whatever they say," he said of the medical staff. "Next is probably just waking up tomorrow and go from there."