PITTSBURGH -- The Pirates placed closer Keone Kela on the injured list on Thursday, a source confirmed to MLB.com on Friday, making it likely that Pittsburgh's top reliever will not be available for the start of the season.

Kela has not been able to participate in any of the Pirates' Summer Camp workouts this month. The club has said it cannot disclose the reason for Kela's absence, and manager Derek Shelton reiterated Friday afternoon that he can’t share anything about Kela’s status.

Kela and No. 2 prospect Ke’Bryan Hayes have been sidelined for the entire camp with no explanation provided by the team. Kela was placed on the injured list without a specific injury listed.

Major League Baseball has instituted a COVID-19 list this season, although clubs will not announce which players are placed on it due to privacy laws regarding individuals’ health. Players may address their status if they wish, though they are not required to do so. Merely being placed on an injured list without further explanation is not confirmation that a player has tested positive for COVID-19. For example, potential exposure to a person who has the virus can be sufficient cause. According to MLB’s 2020 Operations Manual, there is no minimum or maximum length of placement on the COVID-19 related IL.

The Bucs have confirmed positive COVID-19 tests after receiving permission to do so from three players: reliever Blake Cederlind, who has not been active in camp; outfielder Socrates Brito, who returned to PNC Park earlier this week; and right fielder Gregory Polanco, whose positive test was disclosed Friday afternoon.

Starting the season without Kela would be a blow to Pittsburgh's bullpen. Shelton named the 27-year-old right-hander the team's closer after its first Spring Training workout, believing Kela earned the title after posting a 2.12 ERA and a 1.01 WHIP with 33 strikeouts in 29 2/3 innings during an injury-shortened 2019 season. Kela also has experience in the ninth inning, having served as the Rangers' closer before he was traded to the Pirates on July 31, 2018.

As long as Kela remains on the injured list, Shelton said, the Pirates won’t name a designated closer in his place.

“I think we will probably play the leverage of the situation,” Shelton said. “I'm pretty sure we won't go with one certain person. … We’ll probably just play by what we feel is the best guy for each situation.”

That should lead to high-leverage work for setup men Kyle Crick, Richard Rodríguez and Michael Feliz. Crick recorded two saves in 2018, when he posted a 2.39 ERA and a 1.13 WHIP with 65 strikeouts over 60 1/3 innings as an excellent setup man, but he struggled through a pitch-tipping issue last season as he put together a 4.96 ERA while allowing 10 homers and walking 35 in 49 innings.

Crick is probably the most likely reliever to step into the ninth inning, however, given his wipeout slider and his competitive attitude. The 27-year-old right-hander has pitched in high-leverage spots before as a setup man, and despite his struggles last season, he struck out 61 batters.

Rodríguez struggled to keep the ball in the park early last season but recovered well enough, recording a 3.72 ERA in 65 1/3 innings over 72 appearances. The 30-year-old righty doesn’t have overpowering stuff, but he showed how effective he can be in 2018 as he came out of nowhere to log a 2.47 ERA with 88 strikeouts in 69 1/3 innings.

The Pirates still believe in the potential of Feliz, the 27-year-old right-hander who came to Pittsburgh in the Gerrit Cole deal, and they’re intrigued by what he did over the final four months a year ago. Following an ill-fated outing as the Bucs' opener against the Dodgers last May 24, Feliz recorded a 2.84 ERA with 57 strikeouts while holding opponents to a .201/.289/.409 slash line in 44 1/3 innings over 46 appearances. Feliz was also prone to home runs, though, giving up nine during that stretch and 11 overall last season.

Many people in the organization believe right-hander Nick Burdi has the arsenal and mentality of a future closer, but with only 13 appearances over the last two years, he lacks experience in the Majors -- much less in a high-leverage role.