Injuries to Stewart, Justin Topa and Michael Tonkin, along with the news that Rule 5 right-hander Eiberson Castellano won’t make the Opening Day roster, give the Twins a lot to think about in the coming days before the regular season opens at Busch Stadium in St. Louis.

Twins right-hander Brock Stewart reportedly drew a big crowd Saturday when he pitched in a minor-league Spring Training game against the Triple-A team of the Boston Red Sox.

Not necessarily big in terms of the volume of fans in the stands (if there were any stands). But it was really big in terms of who watched.

Bobby Nightengale of the Minnesota Star Tribune reported that manager Rocco Baldelli, pitching coach Pete Maki and general manager Jeremy Zoll personally scouted Stewart’s outing.

And the collective brass decided that Stewart will begin the season on the injured list because of a strained hamstring.

It’s the right move for Stewart, who got off to a late start in February because he was recovering from offseason arthroscopic shoulder surgery. Stewart hasn’t had a complete spring camp, either on the front end, or the back.

Plus, with Stewart still feeling a tug in his hamstring, he doesn’t have enough time for it to fade before the Twins open the regular season against the St. Louis Cardinals on Thursday.

Stewart reported feeling great in his arm this spring, and he had encouraging results in his side sessions and Grapefruit League appearances, but he exited an outing early March 15 when he felt a grabbing sensation in his leg.

There’s no sense in rushing Stewart back just to have the ideal Opening Day lineup introduced at Busch Stadium.

Twins athletic trainer Nick Paparesta told reporters as such when Stewart’s hamstring first started barking.

“We have to keep our eyes open to the end goal here, which isn’t just the start of the season,” Paparesta said. “It’s the whole season.”

Paparesta said it for Stewart’s benefit as much as he did ours. Stewart has been champing at the bit to go north with the team. But the Twins have enough depth to cover an early season absence, even considering Stewart isn’t the only member of the bullpen with an injury clouding the picture.

Right-hander Justin Topa finds himself in a similar position to Stewart as he recovers from a sore shoulder, which first popped up March 5.

He’s working his way back, having appeared in spring games Monday and Saturday, with a bullpen session Thursday tucked between. Topa’s performance recently was particularly encouraging: a scoreless inning with a strikeout, throwing 10 of 12 pitches for strikes.

It should be noted that he was facing hitters who won’t make the Opening Day roster.

Another right-hander, Michael Tonkin, already was ticketed for the injured list because of a strained shoulder. The decision to continue his recovery was easiest among the three.

Topa, like Stewart, has a noted injury history that should encourage the Twins to be prudent, even to excess. Topa might be further down the road to recovery, but he still needs to show that his shoulder is up to the stress. And his sinker velocity (it was 92.9 mph Saturday) still hasn’t recovered from where it was two years ago (95 mph).

Maybe it won’t.

No matter: Two years ago, he was one of the best relievers in the league, his approach is different than any other Twins reliever, and Baldelli is intrigued by having him available to use.

Speaking of bullpen depth, the injuries make for a lot of bullpen decisions over the next several days, as does the news (reported by Dan Hayes of The Athletic) that right-hander Eiberson Castellano will not make the Twins’ Opening Day roster.

The Twins would have to return him to the Phillies, or expose him to waivers, if a trade isn’t worked out. Castellano performed better against the Blue Jays on Saturday, going two innings without allowing a run, but he allowed 10 walks in 10 2/3 innings this spring.

It’s pretty clear his ideal path to the majors requires more time in the minors.

The injuries, along with Castellano’s pending departure, open a spot (or multiple spots?) for someone like left-hander Anthony Misiewicz or righty Scott Blewett to join the Opening Day squad. Both have had strong springs.

But keep in mind two details about Misiewicz and Blewett: They are non-roster invitees and would need to have a spot on the 40-man roster cleared. Transferring right-hander Matt Canterino to the 60-day IL would do it.

There’s more, though; both Misiewicz and Blewett have no more minor-league options, which means they’d be subject to being lost on waivers if the Twins wanted to demote them to the minors. Therefore, Hayes speculates, the Twins could scour the waiver wire looking for temps.

These roster contructors, they sure earn their salaries.