"Obviously, we were hopeful and thought maybe he could rehab through this, but after throwing today, he just realized it's not getting any better," Mozeliak said before the Cardinals played the Brewers at Miller Park.
Motte said on Tuesday that the elbow had responded well to his latest throwing session, which included tosses from 60 and 90 feet. But when Motte threw again on Friday, he did not feel comfortable, Mozeliak said.
"He was making gradual process, but what ended up happening as we started to push him more and demand more from him, today he just got to the point where he couldn't go any further," he said.
Motte saved 42 games for the Cardinals last season, his first as a full-time closer. He went 4-5 with a 2.75 ERA and 86 strikeouts over 72 innings.
The recovery time for the surgery typically is about a year.
"He hasn't even had surgery yet, but generally that's what it is," Mozeliak said.
Without Motte, St. Louis initially turned to Mitchell Boggs in save situations, but Edward Mujica has taken over of late and converted all seven of his opportunities. Boggs was optioned to Triple-A Memphis on Friday, and Carlos Martinez, the team's No. 3 prospect, had his contract purchased from Double-A Springfield.
The Cardinals' bullpen is 0-5 with a 5.90 ERA, the highest in the Major Leagues.
"I still think we have a lot of talent in that bullpen, but clearly, we have to find the right combination that becomes more effective," Mozeliak said. "You don't want to have an inning like we did last night where you have to use three pitchers to get three outs. That's just not efficient.
"I feel like we're going to the same couple guys every night to do that, and my fear is we're going to wear out a Rosie or a Mujica," he said. "That's what we have to be careful of. Making changes is part of what happens when you're struggling."
Martinez will pitch out of the bullpen.