MINNEAPOLIS -- Alexi Casilla is happy to be back in The Show, but knows he has to demonstrate he's improved as player from a year ago, or even this past spring, if he wants to remain in a big league uniform.

Casilla was called up from Triple-A Rochester on Saturday to replace Nick Punto, who was placed on the 15-day disabled list with a strained left hamstring. Casilla hit .219 for the Red Wings this year, but he is hitting .346 over his past 10 games.

Since Casilla can play both second base and shortstop, he was the logical choice to fill Punto's spot on the roster, said Twins manager Ron Gardenhire.

"He's the guy they recommended, [and] I think that is probably right," said Gardenhire. "We all know the ability is there. He's a middle guy. When you go get a middle guy, he's best of all those guys down there and the most talented."

Last season, Casilla seemed to be the heir-apparent at second base for the Twins after Luis Castillo was traded away, but a .222 average in 2007, a mediocre Spring Training, an offseason trade that brought Brendan Harris to Minnesota and the signing of Adam Everett are all factors that have jeopardized Casilla's future in the organization. He said he knows he will have to produce to ensure he is able to continue to wear a Twins uniform.

"I have to keep working hard every day," he said.

Casilla said he has tried to work on the things, mainly defense, that will give him a better opportunity to stay in the big leagues.

"The first thing was my defense," said Casilla. "They told me not to be too fancy. I feel right now I am more comfortable."

Despite his demotion to Rochester this spring, Gardenhire said Casilla remains a valuable infield prospect for the organization.

"He is still in our plans," said Gardenhire. "He's got a cannon, he's got quick feet. He's definitely one of our best prospects."