CHICAGO -- When the Twins traded Luis Castillo to the Mets, the team said it was a chance for Alexi Casilla to show what he could do as a starting second baseman.

Yet Casilla was not in the starting lineup for the Twins again on Friday night. Nick Punto got the nod at second. It's been a trend of late, as Casilla has started just two of the club's last six games at second base.

Mistakes have plagued Casilla early in his tenure as the club's second baseman. But Twins manager Ron Gardenhire said the time off was not a punishment, but a case of pitching matchups.

"With Casilla, I pick my spots on certain pitchers and go from there," Gardenhire said. "Right-handed, I think he's pretty good. Left-handed, he has some issues."

Casilla's struggles from the left side have been noticeable. He has a .182 average when hitting left-handed compared with a .324 average from the right side. The team also has noticed Casilla's tendency to slug bunt when hitting from the left side in an attempt to get hits.

That's something that Gardenhire doesn't want to see from the young infielder.

"He has to get the slug bunt out of his system," the skipper said. "When I see it, I about fall out of my chair every time. He doesn't do it right-handed. If he does, I will fall out my chair."

The Twins aren't about to stop Casilla from hitting left-handed, but they are instead trying to work with him to shorten his swing.

The time off may seem like a disservice to a player trying to learn on the job, but Gardenhire feels the extra time to sit and watch might be beneficial.

"I want to see him more and more, and get a better feel for his positioning, but watching the game sometimes gives you a chance to step back," Gardenhire said. "Hopefully he takes it as a process of learning and watching what the other guys are doing out there."

It's been a slow learning process for Casilla, but one that Gardenhire said he expects will only get better. Despite the abundance of mistakes, Casilla has also showed the club that he can learn from those blunders. Gardenhire pointed to a recent blunder when Casilla was on second and not paying attention to where the ball was hit. He started to run immediately and gave up the base. But the next time, that same mistake wasn't made.

"The next day, there was another ball hit out there and I saw him run and start to go, but he looked around and stayed," Gardenhire said. "He's learning and he's doing better. It's just a process."

Mauer update: It was another day of on-the-field exercises for Joe Mauer, and while he reported progress, it's still unclear whether he will be able to play at all in this series.

"There is still some soreness in there," Mauer said. "As long as it doesn't get any worse and I keep increasing activity, I think that's a good thing."

Mauer did some baserunning on his own after an early batting practice session was canceled. The team did not take official batting practice due to rain, so Mauer's work was limited to his individual running work and hitting in the cage.

As for his ability to play in this series, the catcher isn't eliminating the chance that it might happen.

"It's possible," Mauer said. "It will just depend on if it feels better tomorrow."

Lefty on the way? With the team currently featuring a 14-man pitching staff, the Twins aren't exactly in dire need of more arms.

But the club would make room for that additional pitcher if Glen Perkins proves to be ready. Perkins threw a 10-minute bullpen session on Friday afternoon and reported that things went well.

"I felt really good and I felt strong," Perkins said. "I just kept going until I got tired. And hopefully that will prepare me to pitch at some point this season."

If Perkins is still without any soreness on Saturday, the plan is for him to throw another bullpen session on Sunday and then possibly work his way back into games. And despite the abundance of pitchers, Perkins would give the team another southpaw option. Carmen Cali is the club's only lefty currently in the 'pen due to Dennys Reyes' left elbow problems.

"Obviously, there would be opportunities if I got back," Perkins said. "So that's more motivation for me."

Free your mind: Gardenhire's concern over the catching situation eased a bit on Friday with the arrival of Jose Morales, giving the team two fully healthy catchers on the roster.

Having dealt with only one healthy catcher during the team's final contest against the Indians on Wednesday, Gardenhire admitted that he was a bit relieved not to face that situation again.

"That last game was kind of nerve-wracking, to tell you the truth," Gardenhire said. "Redmond, there was no chance [of him playing], and Mauer was emergency only. Yeah, that's not the way you like to go into a game so it's nice to have another catcher here."

Morales won't be limited to emergency-only duty. Gardenhire said the 24-year-old catcher likely will start Saturday's game and catch for pitcher Matt Garza, whom he paired with at Triple-A Rochester earlier this season.

Twins tidbits: The Twins will stick with a five-man rotation for the rest of the season, so Kevin Slowey will now be used as a long reliever out of the bullpen. Gardenhire said there is still a possibility that Slowey or Nick Blackburn could get a start, but for now both will remain in the 'pen. ... Garrett Jones got the start at DH on Friday night. It's a homecoming for the Chicago-area native, who grew up a White Sox fan and regularly attended games at Comiskey Park. Jones said he had a large contingent of family and friends coming to Friday's game.

Coming up: The Twins and White Sox will face off in the FOX Saturday game for the second of their three contests at U.S. Cellular Field. Garza will face off against Chicago's Jose Contreras in the 2:55 p.m. CT start.