"It's a Grade 3 strain of his groin," Hill said. "We're going to rehab it, and best-case scenario is a six-week return. Obviously, there is still opportunity for G to be back this season's end. But obviously, it was a significant injury and we'll see how rehab goes."
Stanton was injured on the final play of Saturday's 8-7 loss to the White Sox, attempting to stretch a single to a double.
With two outs, he lifted a fly ball to short right field, and Chicago's Adam Eaton was unable to make a running catch. Seeing the ball skip free, Stanton dashed to second base. But before reaching the base, he pulled up and lunged headfirst toward the base.
Shortstop Tim Anderson applied the tag for the final out, and Stanton rolled onto his back for a few minutes before he slowly walked back to the dugout, and he was limping when he left the ballpark later that night with manager Don Mattingly.
"In a long season, things happen," Hill said. "Things always happen. That's what Donnie talks about with his team, that over the course of 162 games, things are going to happen, and we have to have the wherewithal in that clubhouse and the depth in our system to try to absorb whatever comes our way.
"Obviously, G is a big part of our club, and we've dealt with a lot already. We'll deal with this, and we'll get through it, and we'll be OK."
With Stanton out, Ichiro Suzuki will play more regularly in right field.
The club also is exploring some players from outside the organization, including Carlos Gomez, recently designated for assignment by the Astros. Alex Rodriguez was considered, but his publicist announced on Monday that he would not be returning to the field this season.
"It means we've got to find another way to win, simple as that," Mattingly said. "We did it early in the year. Giancarlo early in the year was not really contributing, and he wasn't swinging well, but we were able to sustain. I think that's really what we have to do."
The Marlins have endured a rough August, but Stanton has been heating up. He homered and had three RBIs on Saturday, and in his past seven games, he was batting .280/.333/.680 with three home runs and nine RBIs.
The 26-year-old is batting .244/.329/.826 with 25 homers and 70 RBIs in 103 games.
Staying healthy has been a challenge for Stanton, who appeared in just 74 games in 2015 due to a broken left hamate bone. And in 2014, when he paced the National League with 37 homers, Stanton's season ended on Sept. 11 after he was struck in the face by a Mike Fiers fastball at Milwaukee. He played 145 games that year.
"Obviously, you're disappointed," Mattingly said. "You lose that out of your lineup. It looks like it's going to be for pretty much the rest of the year. You're disappointed, but it's one of those things that you talk about as a ballclub from Spring Training forward. Nothing can get in our way. You've just got to move forward."
The club is already without power-hitting first baseman Justin Bour, who has not played since July 2 due to a sprained right ankle. Bour has 15 home runs and 46 RBIs, and he's not expected back until September.
All-Star center fielder Marcell Ozuna, who has 19 homers and 60 RBIs, is now being asked to hit cleanup.
"Injuries are going to be part of it," third baseman Martin Prado said. "[Stanton] did it just trying to be aggressive on the bases. There's nothing wrong with that. He feels disappointed. We need that guy in the lineup. We've got to have a couple of guys step up for him, and we're going to keep going until he gets better."
Fantasy spin | Fred Zinkie
Expected to miss the remainder of the regular season, Stanton will undoubtedly leave a massive hole in fantasy lineups. Wise owners will analyze their league standings to determine if they can get by with a waiver-wire replacement, or if a trade for a premium slugger is necessary. Those who prefer a reliable veteran can search the waiver wire for Brandon Moss, Danny Valencia or Jayson Werth. As for owners who wish to take a chance on a high-upside youngster, consider Jorge Soler or recently promoted Yankees prospect Aaron Judge.
Joe Frisaro has covered the Marlins for MLB.com since 2002. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.