Justin Masterson is no longer part of the St. Louis Cardinals' rotation.

The struggling right-hander, picked up by the Cardinals before the trade deadline, won't make his scheduled start Thursday and instead will pitch out of the bullpen for the team.

Cardinals manager Mike Matheny said Justin Masterson took the move to the bullpen like "a pro." AP Photo/Jeff Roberson

"We've got him in that mindset already," St. Louis manager Mike Matheny told reporters Monday. "When he'll be actually available to go is still up in the air."

Masterson has made six starts for the Cardinals since they acquired him from the Cleveland Indians in July, going 2-3 with a 7.90 ERA. He's lost two straight decisions, the latest to the Chicago Cubs on Saturday after allowing five runs in 4 1/3 innings.

"[He] gets it. He's a pro," Matheny told reporters. "He understands the game, understands where we are and understands where he is. But we're committed to keep working through this. Maybe this could be something that works for him."

On Tuesday, the Cardinals activated reliever Jason Motte from the 15-day disabled list due to a lower back strain, and added four others to put their active roster at 31 players.

The Cardinals also recalled left-handers Marco Gonzales, Nick Greenwood and Tyler Lyons, and catcher Tony Cruz. One will start in place of Masterson on Thursday.

Lyons and Gonzales were standouts in a doubleheader against the Cubs on Saturday. Lyons had a career-high eight strikeouts, the most by a Cardinals reliever since 1978, in 4 2-3 innings of relief in Game 1. Gonzales worked six strong innings in his first career victory.

Motte has been on the DL since Aug. 2. He was the closer before reconstructive elbow surgery sidelined him all last season and is 0-0 with a 4.91 ERA in 24 games this season.

Information from the Associated Press was used in this report.