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8/10/2013 6:52 P.M. ET

Plans for rotation, Wacha to come Sunday

ST. LOUIS -- The Cardinals have six starters on the active roster, but that doesn't mean they will be going forward with a six-man rotation.

Manager Mike Matheny said Saturday that Michael Wacha's callup was primarily a move to give the starters some additional rest. He said he will announce the club's plans for Wacha and the rotation beyond Adam Wainwright's Tuesday start on Sunday.

"I'm not trying to give Michael any more or less information than what he needs," Matheny said. "And what he needs is you have today to go out, pitch and start a big league ballgame, which is pretty cool for a team that's right in the thick of things. We don't want to cloud it up for him at all."

The Cardinals are taking a cautious approach to the 22-year-old Wacha's work load. They had him on a six-day schedule at times with Triple-A Memphis.

"It's always walking that fine line of enough work and too much," Matheny said of Wacha, ranked by MLB.com as the Cardinals' No. 2 prospect. "You want to give him enough to where they're improving and going on a consistent basis to be ready for next year's challenges, but not too many for this year. There isn't a perfect number, but I think we've been pretty consistent with trying to give him as much time as we could in Triple-A and know that he's ready to go as long as we need him to go today."

As expected, the Cardinals optioned Carlos Martinez, who started Wednesday, back to Memphis to make room for Wacha on the active roster.

Wainwright sees benefit of extra days of rest

ST. LOUIS -- Adam Wainwright has pitched more innings than any other pitcher in the Majors. After 175 2/3 innings, the Cardinals called up rookie Michael Wacha to make a spot start for Wainwright on Saturday, allowing their ace an extra three days of rest.

But if you ask Wainwright, his first instinct would be to decline it.

"As a competitor, your knee-jerk [reaction] is to say it's not important. Give me the ball every fifth day and watch me work," Wainwright said. "I think it's smart sometimes to take a step back so you can take two steps forward. These couple of days now in the middle of August will be pretty beneficial down the stretch. I understand it. My arm responds well to that."

Wainwright threw lightly the first few days after his last start, but has primarily been pushing himself in the weight room and resting his arm before a bullpen session Saturday. He'll get back into his normal routine Sunday in preparation for his Tuesday start against Pittsburgh.

The 31-year-old right-hander has not set an innings limit for himself and said he isn't feeling any added stress from the heavy workload. The most innings he has pitched in one season is 233, a career high he set in 2009.

"Going into the year, I think if you set your limit at 200 innings, you're gonna start getting tired around that number," Wainwright said. "That's why I've never set an innings limit. I don't even know where I'm at. I'll look at that stuff at the end of the year. My job is to go out and pitch as long as I can, and that's what I'm doing."

Wainwright isn't concerned that the additional days off will knock him out of his routine. During the All-Star break, he took all four days off from even throwing a baseball.

"This part of the season, our arms are conditioned, our arms are trained," he said. "One day here, one day there doesn't make a difference."

Beltran back after resting hamstring

ST. LOUIS -- Carlos Beltran was back in the lineup Saturday following a day off after admitting to a minor left hamstring pull he sustained against Philadelphia last month.

"I was running the ball down the line and I just felt like I pulled my left hamstring a little bit on that play," Beltran said. "Since that day, I've been trying to play through it, just some days, I feel better than others."

Beltran said it doesn't hinder him on the field, and that it just will tighten up on him from time to time, which is why manager Mike Matheny gave him the night off Friday.

"Some days it gets tight," Beltran said. "Playing every day, of course it's going to happen. That's why he's trying to get me some days, just to make it feel better."

"This is just the same thing we've been doing all year," Matheny said. "Same kind of conversations in April, you know, how are you feeling? Something didn't feel quite right, so that's when we start changing gears."

Worth noting

Yadier Molina ran sprints, took batting practice and did some catching drills in full catcher's gear on the field before Saturday night's game. Molina is eligible to come off the disabled list Thursday.

"We miss every guy that's not with us," Matheny said. "Whenever we have a guy go down who isn't able to help us, it's a missing piece of the puzzle. We're excited that he's feeling good and excited that it's looking like he's not going to be too far [from a return]."

Shane Robinson (strained right shoulder) went 0-for-4 with a strikeout as the designated hitter for Double-A Springfield on Friday. He is expected to remain with the Double-A club for the final two games of the weekend series as he rehabs a strained right shoulder. Like Molina, Robinson can come off the DL on Thursday.

Daniel Descalso started at shortstop on Saturday. Matheny said the Cardinals are taking a day-to-day approach to the position.

"[Pete Kozma ] is doing a terrific job defensively," he said. "Those times come around when you're just struggling to get something going offensively, which we are and yesterday was a pretty apparent example of that. What can we do to help bolster that a little bit and Danny has been putting really good at-bats [together]. … We're going to try to take advantage of anything we can to get going offensively."

• Matheny said Shelby Miller threw a side session on flat ground Friday and that if the Cardinals decide to have him start against Pittsburgh, he will likely be ready.

"He seems to have no reservations at all. Medical staff seems to be in the same mindset," Matheny said.

Chad Thornburg is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.