SAN FRANCISCO -- Yerry De Los Santos knew his body wasn’t right. He didn’t know his situation was this dire.

The Pirates placed De Los Santos on the 60-day injured list with a right shoulder latissimus dorsi muscle strain prior to their 5-3 loss to the Giants on Friday night at Oracle Park. With 54 days in the regular season remaining, De Los Santos’ rookie season is finished.

• This Buc is learning what instrument??

“That's what it ended up being,” said manager Derek Shelton. “It's unfortunate, because he's come up and he's done a really good job for us.”

De Los Santos didn’t think his ailment was of the season-ending variety.

The right-handed reliever said he felt tightness prior to his outing in Arizona on Thursday, one in which he allowed four runs without retiring a batter, but tried to push through. De Los Santos didn’t feel any pain on the mound but said, through team interpreter Mike Gonzalez, “It was like something was there tugging.”

De Los Santos thought this injury was on the minor side, but an MRI said otherwise.

“You just feel bad, because the kid was having a nice year,” Shelton said. “But, yeah, I think after we got the imaging, we realized it was best for him.”

A nice year, indeed. Before the outlier outing against Arizona, De Los Santos had posted a 3.51 ERA and 3.67 FIP across 25 2/3 innings, with 26 strikeouts to eight walks. Those numbers are far more representative of how his season went than his 4.91 ERA and 4.02 FIP, his final season totals.

As De Los Santos’ first season progressed, he pitched his way into a high-leverage role. The rookie’s gmLI, or average leverage index when he entered games, was 1.51. (For context, an average leverage index is 1.) That figure was the third-highest among Pirates relievers who threw at least 20 innings, behind only Wil Crowe (1.58) and David Bednar (1.81).

“I think we saw him grow from the time that he joined us,” Shelton said. “We saw so many positive things, and when we talked to him today, those were the things we highlighted. Those were the things we want him to go into the winter on. Moreso the fact, with a young player, appreciate how he went about describing where he was at and how he felt. It's really important how these guys communicate.”

With De Los Santos out, Pittsburgh’s late-inning options have further thinned. Along with De Los Santos, Bednar remains on the injured list. On Wednesday, director of sports medicine Todd Tomczyk said that Bednar, who has been bothered by a lower back issue since early July, has yet to resume throwing.

Among those on the active roster, Crowe, who has three saves this season, remains a viable option. Manny Bañuelos has only allowed one earned run in his last 11 innings (0.82 ERA) with 11 strikeouts. Colin Holderman hasn’t allowed a run in 7 1/3 innings since coming over from the Mets, but he has given away seven free bases via walk (five) and hit by pitch (two).

“More than anything, just how hitters at this level are different,” De Los Santos said. “Every hitter is different. How to attack hitters, the planning, the speed of the game, how important it is to make sure that you’re constantly learning because the game is growing -- there’s constantly things changing and happening. …

“These are things that I’m going to take with me going into the offseason, get healthy, get better and come back next season fully healthy and ready to help this team win.”