Astros general manager Jeff Luhnow couldn't be reached for comment.
Some of the other intriguing names who will be in big league camp are outfielder Delino DeShields Jr., right-handers Mike Foltynewicz and Nick Tropeano, first baseman Japhet Amador and outfielder J.D. Martinez.
Seven of the Astros' top 10 prospects, as ranked by MLB.com will be in attendance at Major League Spring Training, including Correa (No. 1), first baseman Jon Singleton (No. 2), Springer (No. 3), Appel (No. 4), Foltynewicz (No. 6), DeShields (No. 7) and outfielder Domingo Santana (No. 9).
It's not uncommon for teams to invite their top prospects to get a taste of big league camp, even though most won't make the club to start the year.
The four Minor League free agents are outfielder Adron Chambers, infielder Cesar Izturis, right-handed reliever Peter Moylan and infielder Gregorio Petit.
The other non-roster invitees are right-handers Jake Buchanan, Rhiner Cruz, Jorge De Leon, Bobby Doran and Jason Stoffel, catchers Rene Garcia, Tyler Heineman and Carlos Perez, outfielders Leo Heras and Preston Tucker and infielders Ronald Torreyes and Jonathan Meyer.
Chambers, 27, played in 25 games for the St. Louis Cardinals last season, his third straight year with action in the Majors. He spent the majority of his season at Triple-A Memphis, hitting .252 with 13 doubles, eight homers, 43 RBIs and 16 stolen bases.
Moylan, 35, made 14 appearances across two Major League stints with the Dodgers last season. He spent the majority of his 2013 campaign at Triple-A Albuquerque, posting a 4-1 record with four saves and a 2.74 ERA in 38 appearances.
Moylan has pitched in the Majors in each of the past eight seasons with Atlanta (2006-12) and Los Angeles (2013), making 309 career relief appearances and posting a 21-9 record and 2.80 ERA.
Petit, 29, is joining the Astros from the Padres organization, where he hit .292 with 26 doubles and 61 RBIs in 134 games at Triple-A Tucson last season. He also posted solid numbers in winter ball, hitting .312 with 12 doubles, 10 homers and 27 RBIs with Caracas in the Venezuelan Winter League.
The Astros' current Spring Training roster sits at 64 players (33 pitchers, 31 position players), and the 40-man is full. Pitchers and catchers report to Kissimmee, Fla., on Feb. 15 and position players on Feb. 19.