The outfielder had surgery Thursday on his broken right jaw after being struck by a pitch. The team has not said how long he will be out, but he could miss the rest of the regular season.
Atlanta has a commanding lead in the NL East and hopes Heyward will recover in time for the playoffs.
Dr. Glenn Maron operated on Heyward in Atlanta, one day after he was injured in New York against the Mets. Plates were inserted in both places where the jaw was fractured - along the right side and near the chin.
"We haven't talked time frame," Gonzalez said. "It wasn't wired shut. That's a good thing."
Before his injury, Heyward had become one of the Braves' hottest hitters. He was batting .253 with 13 homers and 37 RBIs. Plus, he's one of baseball's top defensive outfielders.
"He's a tough one to replace," Gonzalez conceded.
The loss of Heyward is the latest in a staggering string of injuries for the Braves this season, even while building a 15-game lead before the series in St. Louis.
"We've just got to find a way to pick up where he left off," center fielder B.J. Upton said. "We've got the personnel to fill in and pick up the slack."
Heyward got off to a slow start this season, his struggles heightened by an emergency appendectomy in late April. But he sparked the offense after moving to the top of the batting order last month, filling a role that had been a major problem.
"You just don't replace an outfield piece like that," said utilityman Evan Gattis, who likely will take on a bigger role. "It's a big loss. We'll battle it out and see what happens."
The Braves have relied largely on stellar pitching to carry them to the top of the division, ranking second in the league in ERA (3.18) before they faced the Cardinals.
Upton and second baseman Dan Uggla are in the midst of dreadful seasons, both hitting under .200. Uggla is on the disabled list recovering from laser eye surgery. Outfielder Reid Johnson is also on the DL with an Achilles tendon injury and the Braves aren't sure when he'll return.
Barring a trade, the Braves will have to get by with a makeshift lineup. In Thursday night's game, the Braves went with Jordan Schafer in the leadoff spot and playing center field, started Gattis in left and shifted Justin Upton to Heyward's spot in right.
B.J. Upton did not start.
Also, the Braves claimed infielder Elliot Johnson off waivers from Kansas City, reinstated pitcher Paul Maholm from the disabled list and optioned infielder Phil Gosselin back to Triple-A Gwinnett. Johnson started against the Cardinals.
"We'll just all have to step up," Justin Upton said. "We know what we have to do."
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