The Houston Astros are just three weeks into the season and they already will have used eight different starting pitchers when Spencer Arrighetti toes the rubber against the Colorado Rockies on Wednesday at Daikin Park. Half of those starters currently reside on the injured list.

Cody Bolton made it four starting pitchers on the injured list Thursday when he was placed on the 15-day IL with right mid-back inflammation. The move with Bolton opened up the roster spot for Arrighetti, who was called up from Triple-A to fill in to the depleted starting rotation.

Hunter Brown, Cristian Javier and Tatsuya Imai — three of the first four pitchers in the rotation when the team opened the season — all have been placed on the injured list in the past 10 days.

Astros manager Joe Espada said he doesn’t recall another rash of injuries so early in the season like this, but added, “Today’s a new day. We’ve got an opportunity to win a series and that’s where our entire focus is.”

Bolton was pushed into action after the injuries began to mount, but he was struck in the back by a line drive in his first start last week in Colorado. He made his next start against the Seattle Mariners but was removed in the second inning when his back began to tighten.

“The area of the line drive he took, still sore, so we’re not going to have him throw for a couple days until that general soreness goes away,” Espada said.

Ryan Weiss will make his first big league start in Thursday’s series finale against the Rockies, and then Lance McCullers Jr., would be on track to start the series opener against the Cardinals on Friday. After that, the only other healthy pitchers who have started games this season are Mike Burrows and Colton Gordon, who started Tuesday.

That leaves an opening for someone like Arrighetti to turn Wednesday’s start into several more.

“This is your opportunity to shine,” Espada said of players having to step up for the injured. “My message in spring training was that, ‘Hey if it’s one inning, one outing, one at-bat, one play, make a difference to help us win.’ And today’s an opportunity for someone else.”