SAN FRANCISCO -- Less than a week after promoting Camilo Doval, the Giants added yet another young fireballer to their bullpen, calling up fellow relief prospect Gregory Santos ahead of Thursday night’s series opener against the Marlins at Oracle Park.

As expected, second baseman Donovan Solano was placed on the 10-day injured list with a right calf strain. Solano, 33, sustained the injury while running the bases in the sixth inning of the Giants’ 6-5 loss in Philadelphia on Wednesday. An MRI exam confirmed the severity of the injury, though manager Gabe Kapler said the Giants still haven’t determined a timetable for Solano’s return.

“We’re still kind of going through the initial examination period,” Kapler said. “Last night, he wasn’t great getting off the plane. I know that today he’s feeling a little bit better. I don’t really want to go out too far in advance.”

The absence of Solano, the reigning National League Silver Slugger Award winner at second base, is a blow to the Giants, as the native of Barranquilla, Colombia, had been one of the club’s most consistent and productive bats to start the season.

Tommy La Stella started at second against Marlins left-hander Daniel Castano on Thursday, but Kapler said Wilmer Flores and Mauricio Dubón could also draw reps there while Solano is out. Still, the decision to add another pitcher to the 26-man roster will leave the Giants short-handed on the bench, which has been one of the strengths of the club so far.

Brandon Belt (right quad soreness) and Brandon Crawford (rib cage tightness) are also banged up, but Kapler said he was hopeful the veteran infielders would be available off the bench on Thursday, and Crawford struck out as a pinch-hitter to end the seventh inning, staying in to play defense. Flores and Dubón started at first base and shortstop, respectively, against Castano.

The Giants needed extra bullpen help after starters Logan Webb and Anthony DeSclafani each lasted only four innings in their previous two games against the Phillies. Santos, 21, hadn’t pitched above Class A Augusta, but the Giants wanted another righty in their bullpen to give them more late-inning options against the Marlins’ right-handed-heavy lineup.

He made his Major League debut with a 1-2-3 sixth inning in Thursday's 3-0 victory, striking out the first two batters he faced. Acquired from the Red Sox along with Shaun Anderson as part of the Eduardo Núñez trade in 2017, Santos was touching 101 mph while working in relief at the Giants’ alternate training site in Sacramento.

“Obviously, the velocity is encouraging, but all the velocity in the world doesn’t help if you’re not able to attack the strike zone,” Kapler said. “The fact that he’s throwing his slider for strikes gives us confidence here. He’s also been built up enough to potentially be more than one inning, potentially one-plus.”

Santos, who is ranked the club’s No. 13 prospect by MLB Pipeline and hails from San Cristóbal, Dominican Republic, said he received a phone call from the Giants at 10:45 a.m. on Thursday informing him that he’d earned his first big league callup. He was added to San Francisco’s 40-man roster along with Doval and Kervin Castro in November, but he admitted that he didn’t expect to be in the Majors only three weeks into the 2021 campaign.

“I feel really good after taking another step forward in my career,” Santos said in Spanish. “I didn’t think that they were going to call me up this fast. I knew I was doing good work at the alternate site, but I didn’t think I would get this opportunity so soon.”

Santos was primarily a starter in the Minors, but he opened eyes after moving to the bullpen during instructional league last fall. Kapler didn’t rule out the possibility that Santos could be given the opportunity to start again in the future, but for now, the Giants will be hoping he’ll be able to bolster the back end of the bullpen and help bridge the gap to setup man Tyler Rogers and closer Jake McGee

“It’s still the same baseball, just a little bit different,” Santos said of his new role. “Before I’d have five days to get ready. Now I have to be physically and mentally prepared every day.”

In San Francisco, Santos will reunite with his close friend Doval, who also pairs a high-octane fastball with a nasty slider. Santos watched Doval’s debut against the Marlins on Sunday and said he thought his countryman “looked like a veteran” in the electric outing. Doval, 23, has already been trusted to handle high-leverage situations for the Giants, and Santos could be in line for similar opportunities this week against the Marlins.

"The potential for both of these guys and Kervin Castro, as well, is for all to stick in a Major League bullpen," Kapler said. "I think that's part of the reason they're on our 40-man roster. It's exciting that Santos is going to have his opportunity to make his Major League debut, and Doval has already had three appearances. It's nice to get their feet wet and see how they can contribute."