KISSIMMEE, Fla. -- They represent the future of the Astros and should be a big part of the core of whenever the organization returns to contention.

Astros fans hoping to see outfielder George Springer and first baseman Jon Singleton -- two of the six prospects sent packing from Major League camp on Thursday -- in the lineup at Minute Maid Park on Opening Day will have to wait a little while longer.

Springer, the team's No. 3-ranked prospect, was reassigned to Minor League camp, along with right-hander Mark Appel (No. 2), shortstop Carlos Correa (No. 1), outfielder Delino DeShields Jr. (No. 7) and right-hander Mike Foltynewicz (No. 6). Singleton, the No. 4-ranked prospect in Houston's system, was optioned.

"Today we talked to a lot of players that represent the future of the Houston Astros," general manager Jeff Luhnow said. "It was a good experience for all these players to come to camp and spend the time they did with our Major League staff.

"As we're looking at a week from today flying [to] San Antonio [for a pair of exhibitions], we're trying to make sure we're giving the Major League at-bats to the guys that are going to be on the team [on] Opening Day, and this is the time we do that.

"We did have the luxury of keeping some of these players longer than they might have stayed in years past with other organizations, but I think that was ultimately a benefit to them and to us."

Of course, the one name that resonates with Astros fans more than any other is Springer, who put up huge numbers in the Minor Leagues last year. Luhnow had hinted all winter that Springer would begin the season in the Minor Leagues, and it didn't help that the high-flying outfielder batted .161 with one RBI, four stolen bases, eight walks and 11 strikeouts in 14 games this spring.

"In the case of Springer, we feel he's very close," Luhnow said. "And we do believe that Springer is going to spend most of this year in Houston. He should, barring injury or any setbacks.

"We want him to play right field, because that's the position he's going to play when he gets to Houston. It's not a huge change from center, but it is different, and you need to get some reps out there. I think we've seen early in spring he had a few difficulties, and as the spring has gone on he's gotten more comfortable out there."

Springer, 24, was clearly disappointed as he left Major League camp. He'll begin the season at Triple-A Oklahoma City.

"There's obviously some stuff I can improve on," he said. "I'll go down there, and that's what I'll do."

When asked if his goal was to reach Houston this year, Springer said he can't look that far ahead.

"I'll just go out and play hard and continue to handle myself the way I know how, and just be professional and play hard," Springer said. "Just go out there and play and keep developing, and at the end of the day, whenever the opportunity comes, just try and kick down a door."

Singleton, who made news early in camp when he disclosed he had spent time in a rehabilitation facility to battle marijuana dependency, batted .154 with one homer and four RBIs and nine walks in 35 plate appearances. He'll start the season at first base at Oklahoma City and could also be in Houston this year.

"Singleton missed some time last year [because of a failed drug test]," Luhnow said. "Is he ready? In our opinion, no. Is he close? Yes. Could it be this year? Absolutely. Could it be the first half of this year? No question about it. We need to let our coaches make that determination when they feel these players are ready, and when the opportunity exists in Houston."

Singleton also has a goal of reaching Houston this year.

"I'm still going to go out and have fun," he said. "That's the biggest part of being successful in this game. If you can't have fun, it's going to become something stressful, and that's not what this game should be about. It should be about having fun and being able to enjoy what you're doing for this limited amount of time we have. Anywhere I play, I'm going to go out and play hard."

Correa, the No. 1 overall pick in the 2012 First-Year Player Draft, thoroughly impressed the staff with the way he handled himself in all facets of camp at 19 years old. He'll likely start the year at Class A Lancaster, but there were some in the organization who wanted him on the big club this year.

"I think any coach that finds himself on a baseball field with Carlos Correa, you would leave thinking that this guy belongs there, because he's that kind of talent," manager Bo Porter said. "At the same time, there's still development in which Carlos needs. He'll go down to the Minor Leagues and continue his development."

Correa took the news in stride.

"It was a great experience," he said. "I came out here with the big league guys. I learned a lot. It was something great for me, for my career."

Foltynewicz, a hard thrower who allowed eight hits and struck out seven in 10 1/3 innings this spring, said the thought of making the club as a reliever was tempting, but the team plans to keep him as a starter, beginning at Oklahoma City.

"They told me they were real pleased with the way I went about my business and my work ethic and all that," he said. "They just said they want my offspeed to be a little more refined, and [for me to] be able to throw the changeup in any count and curveball in any count, and keep the walks down and keep the starting mentality going. They said they really want me to be a starter and get my innings in."

Appel, the No. 1 pick in last year's First-Year Player Draft, was never a candidate to make the big league club, and he never pitched in a Grapefruit League game after undergoing an appendectomy in late January. He's also likely to start the year at Lancaster.

"It's just part of the game," he said. "I knew that I wasn't going to break the camp in Houston to start the season. I knew [getting cut] was going to come sometime. Right now my focus is on tomorrow and trying to pitch live to face hitters and throw an inning or two. I'm just real excited to be able to pitch."

Luhnow has heard the voice of the fans who want to see Springer and some of the others in Houston right away, and he's processed what he's heard from coaches and the staff. Through it all, he's continued to stress patience.

"At the end of the day, we feel like we're making the decision that's in the best interest in the organization and best interest of the player and the team," he said. "All of them have not only potential to be good Major League players, but to be stars in the Major Leagues. There's not too many organizations that can send [out] that caliber of talent all in one fell swoop."