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6/20/2013 7:40 P.M. ET

Despite offensive regression, Castro playing every day

ST. LOUIS -- One year ago, Starlin Castro was batting .302, and headed to his second All-Star Game. The Cubs shortstop entered Thursday's game batting .235 for the season.

"By his numbers alone, he's regressed, there's no question about it," Cubs manager Dale Sveum said Thursday. "You're getting way, way down, as far as all the other shortstops in baseball -- as far as the offensive part. He's under .600 OPS. That would go without saying that he's regressed."

Castro has played every game, and Sveum said he hasn't given the shortstop a breather yet, because he hasn't found a good day. Castro has done well defensively. If he did sit, Cody Ransom would sub at shortstop.

Part of the problem has been Castro's mechanics at the plate.

"He knows the formula," Sveum said. "The rest is up to him. He knows the issues and the mechanical things that are different than when he first got up to the big leagues. It's up to him to get all of that ironed out."

Marmol rebounds with solid outing Thursday

ST. LOUIS -- Carlos Marmol had not pitched in three games since he blew a three-run lead in the ninth against the Mets on Sunday, which resulted in a 4-3 loss to New York.

"I feel great," Marmol said Thursday. "I'm waiting for the opportunity to pitch. We'll see."

On Thursday, the Cubs right-hander was called on to pitch the eighth, and retired the first two Cardinals batters before Pete Kozma reached on an infield single. Pinch-hitter Ty Wigginton then lined out to Marmol to end the inning. It was efficient, which is how Marmol had been in four outings prior to Sunday's implosion.

This season, Cubs manager Dale Sveum has tried to get Marmol back in a game the day after he has a rough outing. Not this time.

"We've got a lot of guys in the bullpen," Sveum said of the Cubs, who have been carrying eight relievers since Saturday, when outfielder David DeJesus was put on the disabled list. "The other times, I did want to get him back on the mound. [Sunday's game], to me, wasn't like some of the other outings. He just got hit [on Sunday] more than imploding and throwing balls all over the place."

Marmol, who has walked 21 and given up 26 hits over 27 2/3 innings, has been working on the side with bullpen coach Lester Strode, who has been with the right-hander since he signed with the Cubs in 1999.

"I've been through this," Marmol said of the tough outing. "I'm working out, talking to Lester. He knows me better than anybody here. We'll see."

In the seven games when Marmol has pitched with zero days' rest, he's posted a 1.35 ERA and is 2-0. Those numbers change dramatically when he pitches on one-day rest. In those 11 games, Marmol is 0-4 with a 15.26 ERA.

"I love to pitch," Marmol said. "I can't make that decision, though. I have to wait for my opportunity."

Extra bases

• Third baseman Ian Stewart's 10-day suspension ends Saturday, and he will rejoin Triple-A Iowa when it begins a four-game series at Memphis. Stewart, 28, was suspended by the Cubs after venting his frustrations about his situation and Sveum on Twitter on June 10.

• The Cubs have eight relievers, and they could make a roster move this weekend to add a position player. They've been carrying an extra pitcher since DeJesus went on the disabled list last Saturday.

One option would be to activate catcher/infielder Steve Clevenger, who was rehabbing at Triple-A Iowa on the 60-day disabled list. Clevenger's rehab time ends Saturday.

• The Cubs have signed two more selections from the 2013 First-Year Player Draft, third-round pick Jacob Hannemann and seventh-round pick David Garner, a pitcher at Michigan State. Hannemann, an outfielder who played at Brigham Young, agreed to a $1 million bonus, which is $250,000 over the recommended slot, according to Baseball America's Jim Callis.

• Top prospect Pierce Johnson has been promoted from Class A Kane County to Class A Advanced Daytona, and the Cougars have added Cuban pitcher Armando Rivero, who had been working out at the Cubs' complex in Mesa, Ariz. Johnson, the 43rd overall selection in the 2012 Draft, was Kane County's Opening Night starter. He was 5-5 with a 3.10 ERA in 13 games, striking out 74 over 69 2/3 innings. On Sunday, he gave up four hits over seven scoreless innings. He's the fourth Kane County player to move up to Daytona this season, joining Chadd Krist, Wes Darvill and Yaniel Cabezas. Johnson ranks seventh on MLB.com's list of Top 20 Cubs prospects.

Rivero, signed by the Cubs this past spring, turned 25 in February. In his final season in Cuba in 2010-11, Rivero had a 3.06 ERA with 38 strikeouts and 21 walks over 47 innings.

Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.