Manager Mike Matheny said Saturday that breaks in the schedule complicate the process. Among the variables, the Cardinals are off Monday and Thursday, the All-Star break is just a few weeks away and rookie Shelby Miller's work load is being monitored.
"We've drawn up easily a dozen models already, trying to think of the pros and cons of each," Matheny said. "If there's a start to be had if will be Joe Kelly's.
"We don't have to make a decision today, so we're not going to."
The Cardinals could use some pitchers on normal rest and give others extra days off. Matheny also said Kelly could be bullpen insurance after three or four days.
The 25-year-old Kelly made 16 starts as a rookie last year in place of the injured Jaime Garcia and was 5-7 with a 3.53 ERA. He has been used in long relief this season with long gaps of inaction, and before replacing Tyler Lyons in the second inning Friday against Texas he'd thrown just 2 2-3 innings since June 5.
"That role doesn't suit just anybody," Matheny said. "I know that's not what his end goal is, to be that. But he has certainly been extremely valuable to us."
Kelly was 0-3 with a 4.22 ERA working 32 innings in 21 games. He got the job after Lyons, who walked three Friday including pitcher Derek Holland, was optioned to Triple-A Memphis on Saturday.
The 25-year-old Lyons won his first two career starts but was 0-3 in his last four and is 2-3 with a 5.51 ERA. He was a ninth-round pick in 2010.
"He needs to control the strike zone with his fastball," Matheny said. "We gave him a list of a couple of little things to work on, but for the most part it has everything to do with fastball location."
Right-hander Michael Blazek, a 35th-round draft pick in 2007, was recalled to add bullpen depth. The 24-year-old Blazek made it to the majors for the first time earlier in the season but did not appear in a game, and had a 2.31 ERA and one save at Memphis in eight games with four of his outings lasting two innings.
He began the year at Double-A Springfield, where he had a 0.92 ERA with 25 strikeouts in 19 2-3 innings.