CLEARWATER, Fla. -- Noah Song came to Phillies camp last month as the longest of longshots to make the Opening Day roster.

It won’t happen now, but it does not mean Song’s time with the Phillies is finished.

The Phillies said Saturday morning at BayCare Ballpark that Song, whom they selected in the Rule 5 Draft, will not throw a baseball for at least a few days because of back tightness. Song had an MRI exam on Friday, they said. It is an interesting development, since Song needs to spend at least 90 days on the Phillies’ active roster to remain in the organization beyond 2023. That does not include time spent on the injured list or on a rehab assignment, which can be a maximum of 30 days for pitchers. Song cannot be optioned at any point.

“It’s just something that happens, I guess,” Song said about the injury. “It kind of came on gradually, I guess, a couple days ago. It’s just something that they wanted to be very cautious of and aware of. We’re just going to monitor it as time goes on.”

The Phillies said Song will not be ready to pitch by Opening Day, indicating he will open the season on the IL.

It will give him more time to ramp up under the Phillies’ supervision. A subsequent rehab assignment will allow him to pitch competitively for the first time since 2019. Song, 25, has not pitched in a competitive situation since then because of his commitment with the Navy, where he trained with the P8-Poiseodon as a Naval Flight Officer. Song had a 1.06 ERA in 17 innings with Single-A Lowell in 2019. People believed then that he could be a top-of-the-rotation starter -- including Dave Dombrowski, who was with Boston at the time.

Song requested 10 months ago to have his service transferred from active duty to selective reserves. The Navy granted the request last month, restarting Song’s once promising baseball career.

The Phillies want to see if Song can still be a top-shelf starter.

Song is curious, too.

He said he has thrown three or four bullpen sessions since he arrived at camp. He was supposed to throw one on Friday.

“They didn’t feel that they wanted to push it through a bullpen,” Song said. “So, they just chose to play it out and take some more time.”

And those first few bullpens?

“I think it’s been steps in the right direction,” Song said.

Because Song had his service transferred this offseason, he does not need to be placed on the Phillies’ 40-man roster until Opening Day. The Phillies could place him on the 60-day IL to start the season, which would again keep him off the 40-man roster, although they would have to make the case the injury is serious enough for that. At some point, if Song is healthy and if he does not make the active roster, he can be traded or placed on waivers. If he clears waivers, the Red Sox can take him back for $50,000 and then send him to the Minor Leagues.

The Red Sox almost certainly will take him back, if that happens. They were stunned the Phillies took him in the first place.