JUPITER, Fla. -- Past the point of being concerned about the mild hamstring strain that wrecked a large portion of his Spring Training, Cardinals’ right-hander Sonny Gray said that missing game action for almost three weeks is the primary reason why he will open the regular season on the 15-day injured list.

Rather than breaking camp with the Cardinals as they face a daunting opening against the star-studded Dodgers in Los Angeles, Gray will remain in Florida for much of the next two weeks while he makes three rehab starts. While the Cardinals’ $75 million offseason addition is frustrated, he called it “farfetched” to pitch next week after not working in a Spring Training game since March 4.

“I’m not worried about my leg, but I just need to get into a game,” said Gray, who was officially declared out for the start of the season on Friday by Cardinals manager Oliver Marmol. “I need to face hitters, have an umpire, have a pitch clock, and have a defense and pitch in a game. I think it’s farfetched to say, ‘You’ve thrown 50 pitches and an up-down in a bullpen and faced hitters with coaches standing behind you and no defense' … . This isn’t even about the health part; I’ve got to get into a game and pitch in a game.”

On a day when the Cardinals-Marlins Spring Training game was canceled because of rain, Marmol also revealed that Lars Nootbaar (rib fractures) would join Tommy Edman (wrist), Keynan Middleton (forearm strain) and Drew Rom (biceps strain) on the injured list to start the season. Nootbaar, who recently started swinging a bat and doing some rotational work, will be reevaluated by doctors again on Saturday to determine if he can increase the intensity of the rehab from a freak injury suffered when his elbow jammed between the outfield wall and his abdomen.

Zack Thompson, who came to Spring Training insisting that he wanted to be a starting pitcher even though the Cards already had five starters under contract, will take Gray’s spot in the rotation, Marmol said. Thompson beat out fellow left-hander and close friend Matthew Liberatore for the No. 5 starter’s job by posting a 2.81 ERA over 16 innings of Spring Training action. A lefty who once idolized and imitated Clayton Kershaw’s mix -- which includes a fastball and a curveball -- Thompson added a changeup and a smaller, tighter curveball this offseason to provide himself with more options to throw at hitters.

“I think I’m much more pitcher than thrower this year, to put it bluntly,” Thompson said. “I went from two-ish pitches to five-ish pitches and I’m comfortable throwing them in any count. That forces the hitter into a different approach, and they can’t just sit fastball if I’m not landing the curveball.”

Liberatore will also be on the Opening Day roster, Marmol said, but as a short-burst reliever instead of a starter. Liberatore had success in that role last season, and he said he’s looking forward to pitching in high-leverage situations out of the bullpen.

“I couldn’t be more excited,” Liberatore said. “I said from the get-go this spring that I want to be a part of the team and contribute in whatever way that is and I’m going to get that opportunity. I couldn’t be more ready and excited for it.”

Gray is excited about pitching in games again, and that first opportunity will come on Saturday over two innings against Minor League hitters. He is expected to pitch at least once more in Florida before pitching a game for Triple-A Memphis in early April. If all goes well with those rehab assignments, Gray will likely make his Cardinals debut against the Phillies (April 8-10) at Busch Stadium. By then, he’ll be built up to throw 85 to 100 pitches, which is a much better option than opening with the big league club in an abbreviated start, Gray stressed.

“We went through a bunch of different scenarios,” Gray said. “They gave me some scenarios. … There were ways to not do the IL. But then, you’re looking at it like, ‘You get one start in a Minor League game and you’re jumping into a big league game, and you can throw maybe three innings.’

“It was nice to have the options, and they were very open to [other plans], but it was ultimately my decision to say, I think it’s right if we do the IL thing, I make three [rehab] starts, I get to pitch 10 to 11 games into this [season] and feel confident that I’ve gotten to where I need to be. I’ve felt good throughout [with the right hamstring], but it was just a matter of getting to a game.”