"Tomorrow is the test," Stanton said following the Marlins' 4-0 win over the Brewers at Miller Park. "I'll do all the pregame stuff, practice, run around in the outfield, [batting practice]. We'll see how the pregame goes."
Stanton said the "loose bodies" -- possibly a bone or cartilage fragment -- is six millimeters, or the size of the tip of his pinky.
Stanton wants to compete in the Home Run Derby and All-Star Game, but if he doesn't play on Saturday and/or Sunday, he may decide to not take part in he events.
"I'd rather play Saturday and Sunday," the slugger with 19 home runs and 50 RBIs said. "But that will be a game-time decision. It just all depends on hitting out there, not in the cage."
The 22-year-old wants to be able to participate in the Home Run Derby confident that his knee won't lock up.
"I definitely don't want to go out there and have to come out after five or 10 swings," Stanton said. "It would look real bad."
Thursday was the first time since Monday that Stanton took swings in the batting cage. He said his knee felt, "medium. I don't know either way."
If Stanton doesn't travel to Kansas City for the All-Star events, he could be returning to Miami to have a procedure to remove the loose bodies.
"This is something we knew was day to day, and today is a new day," Marlins general manager Michael Hill said. "We'll see how it feels."
An MRI taken on Tuesday revealed some fragments of bone or cartilage. Guillen will ultimately decide when Stanton is back in the lineup.
"He's not playing tomorrow," Guillen said of the opener at St. Louis. "When he says, 'I'm ready to play,' then we'll see. Nobody can demand to be in the lineup.
"When he's ready to play, I'll be more than happy and pleased to play him. There is no doubt about it. I'm not going to change my lineup from one day to the other because he's ready. When he tells me he's ready, we'll play him the next day."
The Home Run Derby can be seen on MLB.com and ESPN at 8 p.m. ET on Monday. The All-Star Game is on FOX at 7:30 p.m. on Tuesday.
Stanton is giving himself as much time as possible to be in the Derby and All-Star Game, as well as prepare. If he can't go, he notes, the National League will have time to find another player for the Derby.
"You'd love to be in the All-Star Game and the Home Run Derby, so it's not going to be hard to get a replacement," Stanton said. "But in terms of me, I want to go. I'm not really thinking about a replacement."