Tyler Colvin used a rigorous offseason routine to put on 25 pounds. (Getty Images)

MESA, Ariz. -- Highly touted shortstop Starlin Castro will likely open the season in the Cubs' Minor League system. Outfielder Tyler Colvin, though, also has made a good impression this spring. Could he make the Cubs' 25-man big league roster?

"Why not?" Cubs manager Lou Piniella said Saturday. "[General manager] Jim [Hendry] and I haven't sat down and talked about what the organization wants to do as far as everyday playing. We haven't broached that subject. [If Colvin] keeps going the way he is, the subject will be broached sooner or later."

Colvin, the Cubs' No. 1 pick in the 2006 First-Year Player Draft, grew up this offseason, both physically and mentally.

"Colvin is a good-looking player," Piniella said. "It's a big difference that weight he put on. He's got more bat speed, The ball is jumping off his bat. He looks like a Major League player."

Cubs catcher Geovany Soto dropped 40 pounds, and pitcher Carlos Zambrano lost 15 this winter. Colvin, on the other hand, added 25 pounds, working out with team strength and conditioning coach Tim Buss in Arizona. What difference does that make for the outfielder?

"It gets him stronger," Piniella said. "He's whipping that bat through the hitting area pretty good."

It took a while for Colvin to get used to the extra weight.

"I don't feel it anymore," Colvin said on Saturday. "Obviously, I feel strong when I'm hitting. It was really tough when I got it all on and started the running phase around Jan. 1 with 'Bussy.' It honestly felt like, 'Oh, gee, I don't know if I can run with all this.' [Buss] said, 'Don't worry, you'll get used to it.' Now, it doesn't feel like I added 25 pounds. It's normal."

The workouts, which took about two hours per day, focused on his core and legs. Plus, there was a lot of running. Did he want to add the weight, or did the Cubs suggest it?

"Both," he said.

Originally, Colvin, 24, was going to play in Mexico to make up for lost time. He underwent Tommy John surgery in November 2008 on his right elbow and last season played at Class A Daytona and Double-A Tennessee. Player development director Oneri Fleita said the organization thought Colvin could use a real offseason and gave him the choice of working with Buss in Arizona or playing in Mexico.

"It took me about five seconds to give them an answer," Colvin said. "I think it worked out pretty well."

Does he feel a difference when he's swinging?

"Maybe a little bit," Colvin said. "That's the thing with being stronger is that you have more bat control and maybe see the ball a little longer.

"I wouldn't say 25 pounds made all the difference in the world," he said, "but it helps out with your mind, it helps with your confidence and I think that was the biggest thing, to feel big and strong and feel you can do more out there."

Colvin played in six games last season with the Cubs, but at that time, Piniella said the outfielder looked tired after a full Minor League season. He was eating in a restaurant, all packed and ready to go home, when he got the call to the big leagues.

"I just had to move back into the hotel for another night, that's about it," he said.

Colvin denied he was fatigued at the end of last year and said he felt good at the plate.

"I was just a little skinny guy up there," he said.

Something is different this spring.

"It's probably a mixture of everything, getting some at-bats up there last year, getting the confidence up, plus the training I did in the offseason," Colvin said. "I know I'm prepared for this year."

The Cubs need a solid left-handed bat in the lineup. Xavier Nady will be able to hit but will be limited defensively while he continues his rehab from Tommy John surgery. The Cubs are looking at their extra-outfielder options. So, could Colvin make the final 25?

"There's no telling," Colvin said. "All I can do is keep hitting the ball here and make it a tough decision and that's it."