The Brewers announced the extent of the injury following their 4-3 win over the Marlins. Yelich returned to Milwaukee for additional tests on Wednesday.
"The hope is we can provide an update (Thursday),'' Brewers manager Craig Counsell said.
Yelich, 27, was injured in the top of the first inning Tuesday when he fouled a pitch off his kneecap.
Yelich remained on the ground for several minutes before getting up and limping to the dugout.
"First and foremost, we feel awful for Christian. This is a guy who's carried us in a number of ways over the last two years," GM David Stearns said. "He could've [been] two and a half weeks away from a repeat Most Valuable Player award. So that's where our thoughts go first.
"From a team perspective, we've got a lot of guys in that clubhouse who will hurt tonight. This is a gut punch for a night. And then we need to recover and play really strong baseball. We've been through this before as an organization -- two years ago, almost to the day, we lost Jimmy Nelson to a similarly freak injury, and we competed at a very high level for the remainder of that season. And I expect our team to compete at a similarly high level going forward."
Counsell said Yelich was crushed by the news that his season is over and added that the team has to keep battling as it did to win Tuesday's game.
"We have to move forward," Counsell said. "We feel awful for Christian. That's the thing kinda resonating with me right now is he's a special player, and it's a joy to watch him play every day. And he's the best at what he does. So not being able to see that every day is definitely no good. But we gotta respond, and we have a great opportunity, and the guys battled to a great win tonight."
With Tuesday's win, the Brewers moved within one game of the Chicago Cubs in the race for the second NL wild card.
"We battled to a win. And that's what we're gonna have to do the rest of the year is just find ways to do it," Counsell said. "Guys are gonna have to step up, guys are gonna take on bigger roles, and we've got a lot of guys doing good things right now, and that's how we're gonna have to win games."
Yelich ends his season batting .329 with 44 home runs and 97 RBIs and led the majors in slugging percentage and OPS entering Tuesday's games. Yelich has enough plate appearances to qualify for the batting title and becomes just the third player to finish a season with a qualified OPS of 1.100 or higher. In addition to his 1.100 OPS, he's tied for second in the NL in homers, third in batting average and third in stolen bases with 30.
Yelich's 7.1 wins above replacement this season trailed just that of Cody Bellinger (8.2), Mike Trout (8.1) and Alex Bregman (7.4). For the season, the Brewers are 67-63 in games in which Yelich played and 9-5 in games he missed.
"Obviously awful. We all know Yeli and what kind of guy he is,'' said Marlins manager Don Mattingly, who coached Yelich in his final two seasons in Miami before his trade to Milwaukee. "You hate to see a player like that get hurt down the stretch. He's stepped into the superstar realm as a player and MVP last year. You don't want to see that happen to a team down the stretch.''
Trent Grisham, who continued Yelich's at-bat and struck out, took over in right field for Yelich.
Grisham will get additional playing time in Yelich's absence. The outfielder tied a team rookie game record with his five-hit outing Monday, and his double played a role in Tuesday's go-ahead rally.
"A big blow, what he means to this team and the year he's been having,'' Grisham said of Yelich's injury. "We wish him the fastest recovery he can get. It's exciting to help contribute and do my best to help win games.''
ESPN Stats & Information and The Associated Press contributed to this report.