"It's a tough break for David," La Russa said. "We're going to miss him."
La Russa estimated that Freese could return in six to eight weeks, while Freese said the doctor told him eight weeks and Mozeliak said it could take even longer.
"David Freese will have surgery tomorrow, and the extent of the surgery will likely be determined when the surgeon is in there," Mozeliak said. "At this point I think they believe they will end up putting a plate over the fracture, so you're looking at probably anywhere from nine to 12 weeks as far as his return."
Freese has a career .313 batting average with seven home runs and 57 RBIs in 112 games over his first three years in the Major Leagues. He hit .296 with four home runs and 36 RBIs in 70 games in 2010, and was hitting .356 with two home runs and 14 RBIs in his first 25 games this season.
"I'm going to be OK," Freese said. "When it happened, I was thinking about the team. That's what happened last year. I was devastated because I wanted to help the team. The same goes here. I'll get healthy and I'll get back out there and we'll be just fine."
The Cardinals' lineup struggled last season after Freese went out.
"Given how well he has played and also just looking back last year when we ended up losing him, it was really difficult to score runs," Mozeliak said. "I think the difference, though, between last year's team and this year's team is we're a little more balanced and we're a little deeper, so hopefully we can handle this one. But I think the way we have to look at him now is really getting back sometime by late July."
Rookie Daniel Descalso was in the starting lineup playing third base for Monday's game against the Marlins. Descalso is hitting .226 with five doubles, one triple and six RBIs in 24 games this season.
Descalso, who primarily played second base coming up through the Minors, has played third base in place of Freese at times this season. The Cardinals also have veteran utilityman Nick Punto, as well as Tyler Greene, who can play third base in spot duty. Allen Craig, who was activated from the disabled list on Monday, has played third base at times in the Minors.
"I don't think we have an answer right now at the Minor League level where we can just bring somebody up," Mozeliak said. "We really don't want to dwarf somebody's development like [Matt] Carpenter's, for example, by just bringing him up here as a placeholder. We'll see if we can handle this first with the players we have, and if not, we'll have to see if there's another answer."