Also added to the roster were right-handed pitchers Jason Motte, Mike Parisi and Mark Worrell and infielder Jarrett Hoffpauir.
To clear space on the roster, the Cardinals released pitchers Andy Cavazos and Brian Falkenborg.
Tuesday was the deadline for Major League clubs to file their reserve lists. Players on the roster are protected from the Rule 5 Draft, which will take place on Dec. 6 during the Winter Meetings at Nashville, Tenn.
McClellan, a 23-year-old right-hander from Florissant, Mo., is a reliever who was 6-1 with a 1.81 ERA last season in 40 appearances with Class A Palm Beach and Double-A Springfield. He also pitched in the Arizona Fall League and allowed four runs in 7 1/3 innings for Mesa.
Motte, 25, a converted catcher, had 63 strikeouts in 49 innings for Springfield with a 3-3 record, eight saves and a 2.20 ERA in 44 games. He also pitched in the AFL, going 2-0 with a save and 3.00 ERA in 11 games.
Parisi, 24, was in camp with the Cardinals last spring. For Triple-A Memphis, he made 28 starts and was 8-13 with a 4.91 ERA.
Worrell, 24, was an All-Star for Memphis. He worked in 50 games and had a 3.09 ERA with four saves and a 3-2 record.
Hoffpauir, 24, a second baseman, had a hot season at the plate in 2007. After a .345 average in 61 games for Springfield, he was promoted to Memphis and hit .300 in 55 games.
Both released players pitched for St. Louis this season.
Cavazos appeared in 17 games for the Cardinals with a 10.35 ERA; he was 2-5 in 44 games for Memphis. Falkenborg was in 16 games for the Cardinals with a 0-1 record and 4.82 ERA; for Memphis, he was 3-4 and had 23 saves.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.