WASHINGTON -- Sean Doolittle is back with the Nationals in the city he loves and where he enjoyed his best baseball memories, and the southpaw was off to a tremendous start this season. So soreness in his left elbow was an unwelcome development.

In Game 1 of a doubleheader against the D-backs on Tuesday, Doolittle felt soreness during warmups and throughout his outing. He had felt the same dull pain over the weekend in Pittsburgh. The 35-year-old managed to throw a scoreless frame against Arizona, but the arm discomfort told him something was wrong.

A postgame MRI revealed a sprain. He was placed on the 10-day injured list on Wednesday.

Doolittle had not yielded a run over six appearances out of the Nats’ bullpen, retiring the first 15 batters he faced and logging six strikeouts. He added an effective breaking pitch, and was touching 95 mph with his elusive fastball this season.

The left-hander is optimistic that the sprain is not a major issue, but the next two weeks will be crucial to see how the elbow reacts to treatment.

“It’s a possibility,” Doolittle said of a quick return. “The annoying part about this is there’s still some things we don’t know. We don’t know how it’s going to respond to that. Another cliché: I’m going to take it one day at a time here. By the end of those 10 days, we’ll start throwing again and see where we’re at. And it’ll tell us.”

Doolittle’s value goes beyond his pitching to this young team with so many new faces. One of the few connections remaining from the 2019 World Series run, Doolittle is an example to teammates trying to find consistency and shutdown ability every outing.

“It's [incredible] frustration, because aside from the results on the field, I’ve been having so much fun with this group,” Doolittle said. “I love the group that we have. I feel like I’ve really started to get more comfortable in that veteran role where you’re helping the young guys out. You’re talking to them every day and trying to teach a little bit and be a good teammate, and help them along.

“Obviously, the results have been awesome. But just being back in a Nats uniform and [being] back on the mound, and finding my spot again in the clubhouse. I was having so much fun. So I’m going to keep trying to contribute as much as I can.”

Tanner Rainey, Victor Arano, Steve Cishek and Kyle Finnegan kept the Nats in most of their first 13 games, but Doolittle has been the best of the bunch, handing off to the final three innings by shutting down the opponent with clean innings. So to have this setback was tough to take for the veteran with his new-look arsenal.

“I couldn’t stop thinking about it last night,” Doolittle said. “Flew too close to the sun, man. Finally develops a breaking ball and ends up on the IL. It had been a long con. I’d been setting guys up for 10 years without a breaking ball, and I start throwing a break ball now, and look where it got me. I don’t think that’s the reason, by the way.”

Left-handers Francisco Perez and Sam Clay were recalled from Triple-A Rochester for bullpen depth, but manager Dave Martinez knows that they are faced with a difficult task trying to fill in during Doolittle’s absence.

"It's hard. I talked to [Doolittle] last night for a while, and just because of the history that we have together, it was tough,” Martinez said of their emotional meeting. “I told him, ‘Hey, we'll figure it out, you're strong, you have the will to get through this, so just know that you're not alone and we'll get through this together, and we'll see what we come up with.’”