TAMPA, Fla. -- The optimism the Red Sox had for ace Chris Sale as recently as a couple of days ago has turned into trepidation that the lefty might have a significant elbow injury.

After throwing 15 pitches of live batting practice without incident on Sunday, Sale showed up to the park on Monday with soreness in his left elbow, similar to the injury that knocked him out of the final six weeks of the 2019 season.

He was immediately sent for an MRI, and those images are in the process of being sent to Dr. James Andrews in Pensacola, Fla.

"Obviously there's some concern," said Red Sox chief baseball officer Chaim Bloom prior to Tuesday's game against the Yankees. "Knowing how his 2019 went and how important he is to us, there is some concern. But until we have all the information, we don't want to start speculating unnecessarily."

The Red Sox don't want to go into too much more detail until Sale is fully up to speed on the extent of the injury.

Sale politely declined to speak with reporters in Fort Myers on Tuesday, but he said he should have more information on Wednesday.

The plan was for Andrews to review the images and then speak to Sale over the phone.

The Red Sox were already preparing to start the season with Sale on the injured list, but that was merely due to the flu and pneumonia that set him back for two weeks at the start of Spring Training.

The hope was for Sale to slot back into the rotation on April 7 -- the first day he would be eligible. But there seems little to no chance of that happening now, regardless of what the results of the MRI show.

"At a minimum, even if this is fairly benign, we know it's going to set him back to some degree," Bloom said. "How long, I don't know yet. Hopefully it is not a huge concern and doesn't set him back too much. But we know it's going to set him back some."

Sunday marked the first time Sale had thrown to hitters since his final start of 2019, back on Aug. 13 in Cleveland. In a best-case scenario, perhaps Sale's elbow just felt the effects of ratcheting up the intensity to that degree for the first time in months.

"We also know, in the course of this building up [period], when you do hit these milestones, sometimes you can get sore," said Bloom. "He hasn't faced hitters in a long time. And I think to speculate too much would be irresponsible. But needless to say, everything has gone well to this point. This is our first bump in the road. Hopefully it is just a bump in the road. But you can't help but have some concern."

Last August, Andrews examined Sale and determined that the 30-year-old veteran did not need Tommy John surgery. Instead, Sale had a platelet-rich plasma (PRP) shot and was shut down from throwing for the remainder of the 2019 season.

Sale got a clean bill of health from Andrews in November and went about his normal offseason conditioning.

Until Tuesday's revelation from the club, all systems seemed go for Sale to make a strong comeback.

In the aftermath of Mookie Betts and David Price getting traded to the Dodgers, the Red Sox are hoping to build a competitive season around strong starting pitching from the front end of the rotation.

If Sale is out long term, the team will be challenged to have enough starting pitching. Eduardo Rodriguez, Nathan Eovaldi and Martín Pérez are the only three starters sure to be in the rotation for the start of the season.

There is a wide-open competition for the final two spots, and the Red Sox are also considering using openers.

There are no obvious candidates to seize the openings in the rotation. The pool includes Ryan Weber, Brian Johnson, Chris Mazza, Tanner Houck and Kyle Hart, among others. At this point, the club plans on keeping the electric left arm of Darwinzon Hernandez in the bullpen, though he could factor heavily into an opener scenario.

"Well, rotation depth, regardless of if you have five healthy guys or not, it's a concern," said interim manager Ron Roenicke. "You have to deal with it because five starters are not going through a season anymore. So the more the depth you have when these things crop up, whether it's one guy, two or three, you're more able to handle what happens and the length of time that it happens [for]."

Bloom will also continue to look outside the organization to strengthen the rotation.

Two former veterans who once pitched for the Red Sox are still on the free-agent market in Clay Buchholz and Andrew Cashner. Marco Estrada, Matt Harvey, Jeremy Hellickson, Colin McHugh, Danny Salazar, Aaron Sanchez and Ervin Santana represent some reclamation projects available on the free-agent market.

"Even before this, we were not going to stop looking around outside," Bloom said. "It's an area where even when we have five guys you know you can lean on, you're still never satisfied with the depth."

Sale, a seven-time All-Star, is in the first season of the five-year, $145 million contract extension he signed last March.

It could be that the Red Sox already have a good idea of where things are headed with this injury. But they will wait until they have all the results before issuing a diagnosis.

In the meantime, Red Sox Nation will hold its collective breath.

"Our docs have looked at it, but until we have a full picture of what everybody thinks, we don't really want to get into dribs and drabs of info getting out there," said Bloom.