MLB Insider Jeff Passan gives the details on why Red Sox pitcher Chris Sale decided to have his Tommy John surgery now rather than later in the MLB season. (2:02)

Boston Red Sox left-hander Chris Sale will undergo Tommy John surgery, Chaim Bloom, the team's chief baseball officer, announced Thursday.

Sale chose to undergo the procedure now out of fear that delaying it could have caused him to miss significant time in the 2021 season, sources told ESPN's Jeff Passan. Recovery from ulnar collateral ligament repairs in the elbow typically takes 12-14 months, putting Sale on pace to return early in 2021. While the coronavirus pandemic-induced delay to the start of the Major League Baseball season was not a direct cause of Sale deciding to undergo the surgery, sources said, the possibility of a significant number of games missed reinforced the decision.

In a conference call later Thursday, Bloom said the surgery "would have happened either way."

Bloom would not reveal the physician who will undertake Sale's procedure, but said that the operation would happen "fairly soon."

Bloom said Sale started throwing lightly in a batting cage on Friday and Saturday before playing catch Tuesday, when he felt enough pain that he had to stop throwing.

"This is a tough thing for Chris and a tough thing for all of us," Bloom said. "He's an outstanding pitcher. You will not find a more straightforward, accountable person in the game."

Bloom added that Sale has not felt right as far back as the Red Sox's World Series-winning 2018 season, and has been frustrated with his fluctuating velocity over the past year. When Bloom took the job as Boston's top baseball operations executive, he did see Tommy John surgery as an eventuality for Sale.

Even with the 2020 season up in the air due to the coronavirus pandemic, Bloom said the Red Sox hope to contend should baseball start up again.

"Chris Sale is the type of player that you can't just replace," Bloom said. "He is an elite performer and those types of guys are hard to come by. Needless to say, losing Chris for 2020 isn't going to make our task any easier."

Sale, 30, is entering the first year of a five-year contract worth $145 million he signed last spring. He was shut down with elbow soreness last August after the worst season of his career, during which he went 6-11 with a 4.40 ERA in 25 starts. Following an offseason of rest, Sale returned to the mound during spring training but again experienced elbow issues March 1 and was sidelined again.

Sale underwent an MRI on March 3, and the results were examined by Red Sox doctors along with renowned surgeons Dr. James Andrews and Dr. Neal ElAttrache. Interim manager Ron Roenicke said March 5 that neither Andrews nor ElAttrache recommended surgery for Sale's elbow.

Sale elected to undergo the procedure now having received a platelet-rich plasma injection and gone through other nonsurgical rehabilitation methods that apparently didn't help.

The loss of Sale compounds an offseason of change for the Red Sox, who traded star outfielder Mookie Betts, replaced head of baseball operations Dave Dombrowski with Bloom, parted ways with manager Alex Cora after he was implicated in the Houston Astros sign-stealing scandal and were investigated after accusations of sign-stealing malfeasance during their 2018 championship. MLB hasn't announced its results of that investigation.

Sale, who was traded from the White Sox to Boston before the 2017 season, is 109-73 with a 3.03 ERA in 312 career appearances, including 232 starts. He has struck out 30.7% of batters faced, the highest rate in the live ball era (minimum 1,000 innings pitched). After allowing 17 earned runs over his first four starts last season, he pitched to a 3.83 ERA in his final 21 starts and held opponents to a .207 batting average.

ESPN's Joon Lee contributed to this report.