MILWAUKEE -- Though the Twins placed third baseman Josh Donaldson on the 10-day injured list on Saturday with a mild right hamstring strain, both he and the Twins appear to be quite optimistic about his path to recovery.

For one, there's definitely a sense of relief that it's an issue with the hamstring and not with the calf that has been problematic over the last several years. There's also the fact that he went through some strength exercises without pain and was moving around well during Friday's off-day -- to the point where Donaldson described the move as "more precautionary."

The real test will come when Donaldson does some running -- which could come as soon as the Twins' next series, in Detroit. But for now, things appear promising.

"I don't think it's going to take as many as the 10 days as necessary, barring any type of setback in the rehab process," Donaldson said. "I think today and feeling yesterday how I feel, I feel very optimistic about where we’re at right now."

Still, there didn't appear to be any real doubt that the IL move would be necessary after Donaldson sustained the injury while rounding first base on a double in his first at-bat of the season on Thursday. The Twins had always planned to be extremely cautious with their usage of Donaldson early in the regular season, and they want to be completely sure that he's 100 percent before pushing him back onto the field.

"There was going to be some caution working me into the year," Donaldson said. "I'm not probably missing as many games as people may think [with this IL stint] because there were already planned off-days for me to start."

"We're not sitting here thinking he's going to miss a lot of time because of this," manager Rocco Baldelli said.

Brent Rooker was called up from the taxi squad to take the roster spot. Luis Arraez and Miguel Sanó could split time at third for the time being.

Donaldson's isometric exercises on Friday went without problem, and he added an upper-body lift and some throwing on the field before Saturday's game. He hoped to progress to hitting in the cage and adding lower-body lifts and more dynamic movements on Sunday, with the hope of testing the running in the following days.

The 2015 American League MVP is fortunate not to have felt anything in his calf, and in fact, the modified running form that he took on as a result of that injury history might have contributed to this issue. He has focused on using his hamstrings instead of his calves to accelerate and decelerate on the basepaths, and he felt he might have decelerated a little too abruptly on that double.

He's still confident in his new running form -- so long as this doesn't become a recurring issue.

"I feel great about where I was at, and even moreso where my swing was at," Donaldson said. "And that’s kind of part of the frustrating -- that’s going to take me a little bit of time to kind of get a little bit of timing back as far as that’s concerned. At the end of the day, I still feel very positive of how my body has responded in the last couple of days."

Alternate site roster announced

Last season's alternate training site activities were shrouded in mystery, with nobody allowed into the controlled environment, but that will change this year, as Triple-A St. Paul announced Friday that fans will be allowed to purchase $5 tickets in blocks of two to six to watch the workouts at CHS Field in St. Paul.

The first workout took place Saturday morning.

Here's the Twins' alternate site roster:

Pitchers (20): Andrew Albers, Shaun Anderson, Charlie Barnes, Danny Coulombe, Jhoan Duran, Luke Farrell (on taxi squad), Ian Gibaut, Tom Hackimer, Ian Hamilton, Griffin Jax, Derek Law, Robinson Leyer, Ryan Mason, Juan Minaya, Chandler Shepherd, Devin Smeltzer, Glenn Sparkman, Lewis Thorpe, Andrew Vasquez, Brandon Waddell (on taxi squad)

Catchers (3): Caleb Hamilton, Ben Rortvedt, Tomás Telis (on taxi squad)

Infielders (5): Travis Blankenhorn, Nick Gordon, Tzu-Wei Lin, Drew Maggi, JT Riddle (on taxi squad)

Outfielders (5): Keon Broxton, Alex Kirilloff, Trevor Larnach, Rob Refsnyder, Brent Rooker (active)