JUPITER, Fla. -- Trevor Rosenthal and Michael Wacha, two of the organization's more exciting young right-handers, are scheduled to pitch in the Cardinals' Grapefruit League opener against the Marlins on Saturday. First pitch is scheduled for 12:05 p.m. CT.

Both pitchers will be limited to about 40 pitches, meaning that they will toss two innings apiece, if efficient. From there, they will build up their pitch count in subsequent spring starts.

For Rosenthal, the outing will mark his first in a game since he shined in the 2012 postseason. Ranked as the club's No. 4 prospect, according to MLB.com, the right-hander threw 8 2/3 scoreless innings out of the 'pen during the playoffs, and he impressed enough at the Major League level last year to get an opportunity to compete for a big league rotation spot out of camp.

Wacha, the Cardinals' top Draft pick in 2012, prepared for his first Grapefruit League appearance with a live batting practice session on Wednesday. It was the second time this spring that Wacha has thrown live BP.

Though Wacha -- the Cards' No. 6 prospect -- is not competing for a big league roster spot, this will be his first opportunity to pitch in a game environment in front of the Cardinals' Major League coaching staff.

Matheny has not announced his pitching plans beyond Saturday. He also has not confirmed which position players will make an appearance in the Grapefruit League opener.

Sore shoulder delays Miller's throwing sesson

JUPITER, Fla. -- Shoulder soreness prevented Shelby Miller from throwing off the mound Wednesday, though the Cardinals right-hander said he is confident that the tightness will not keep him off the mound for long.

Miller termed the soreness as "normal," noting that he felt it about this time last year, too, during his spring program. It was the fact that the soreness lingered longer than usual that prompted the club to exercise a more conservative approach.

"We're going to give him a day to grab him time in the training room and work on that," manager Mike Matheny said. "We're not too concerned. We're just going to give him a little more time. It's more preventative right now."

Miller guessed that the soreness was the result of going full effort during his live batting practice, which he threw on Saturday. That effort level was one that he hadn't reached since last year. Miller pointed out a key distinction, too: The soreness cropped up not while he was throwing, but afterward.

The issue was not deemed serious enough to warrant Miller scheduling an MRI. On Tuesday, he took an anti-inflammatory pill, which he said helped significantly reduce the soreness.

"I'm just taking it easy," Miller said. "The biggest thing is just they're making sure there is nothing wrong with me. They just want to make sure it's nothing. That's it. It's nothing serious at all."

Miller projected that he could resume throwing on flat ground as early as Thursday. Matheny did not speculate on when Miller will return to the mound.

The club's initial plan was to have the righty pitch in one of the team's first Grapefruit League games. That season begins on Saturday. But because the Grapefruit League schedule is longer this year, Miller will have plenty of time to get his arm ready for the start of the season, even if he gets a few days behind schedule.

"We planned on having Shelby out there pretty early, but we're going to go slow," Matheny said. "We have all kinds of time. This isn't a major issue as much as trying to get ahead of something that is more preventative."

Miller, along with Trevor Rosenthal and Joe Kelly, is competing for the final spot in the rotation. Rosenthal will be the first of the three to throw in a game; Matheny named him the starter for Saturday's Grapefruit League opener against the Marlins.

Miller has been widely considered to be the Cardinals' top pitching prospect since he was taken by the organization in the first round of the 2009 First-Year Player Draft. He made his Major League debut in 2012 and was recently ranked by MLB.com as the organization's second-best prospect heading into the 2013 season.

Worth noting

• Manager Mike Matheny said the club will likely alter the team's workout schedule on Friday to make some time for a short simulated game. If the Cardinals stick with this plan, they will have a coach -- not a player -- pitching to the hitters.

"To have a full intrasquad game with our pitchers throwing, I have zero interest in," Matheny explained. "The guys just don't get much out of it."

• Left-hander Jaime Garcia had another strong live batting practice session on Wednesday. It marked the second time this spring that Garcia has thrown BP to hitters. Garcia continues to have no concerns about his left shoulder, which bothered him for much of the 2012 season.

• Asked on Wednesday if any of the young pitchers had been particularly impressive this spring, catcher Yadier Molina offered a broader analysis: "All of them," he said. "They came in great shape. Many have good velocity in their arm. We have some good young pitchers here. I feel very good about where we are pitching-wise."