NEW YORK -- The Nationals made a pair of roster moves before Monday night’s game against the Mets, to shuffle around a few arms in their bullpen.

They activated left-hander Tony Sipp from the injured list after he missed 11 games with a strained oblique, designated lefty Dan Jennings for assignment to open a spot on the roster for Sipp and claimed right-hander Javy Guerra on outright waivers from the Blue Jays.

Nationals manager Dave Martinez spoke to Guerra by phone Monday while he was en route to meet the team in New York, hopefully to be activated ahead of Tuesday’s matchup at Citi Field. In 11 games with Toronto this season, Guerra allowed six runs in 14 innings (3.86 ERA) with 15 strikeouts and five walks. He has had trouble generating swings and misses this season, however, with a swinging strike percentage at 7.0, below his career mark of 8.3 percent.

For a team desperately searching for help in the bullpen, Guerra will at least provide a fresh arm. In his last outing for Toronto on Friday night, he tossed three scoreless innings with a pair of strikeouts before he was designated for assignment on Saturday.

“He's been in this division,” Martinez said, referring to Guerra’s two years with Miami. “He knows the hitters, so just getting him in here and getting him settled in a little bit. I think he's a guy that gives us a little bit more length as well.”

Sipp, a Spring Training acquisition, returns to fill the role of the Nationals’ matchup left-hander. Martinez believes Sipp’s late arrival to camp led to his slow start to the year, but his last nine games for the Nats showed some improvement. He did not allow a run in any of those appearances, a span of six innings, striking out five and walking three while holding opposing hitters to a .105/.217/.105 slash line and just two hits.

“I think these last 10-to-12 days were kinda good for him, that he was able to take a little breather because he didn't have Spring Training,” Martinez said. “So he feels really good. He had an outing the other day and was up to 93 [mph]. So he says his arm feels good and he's ready to go.”

Sipp entered in the eighth inning of Monday's 5-3 loss to the Mets, giving up a single to lefty Dominic Smith.

Jennings signed a Minor League deal with the Nationals after the start of the season and made eight appearances for Washington in the big leagues, giving up eight runs (seven earned) in 4 2/3 innings with nine strikeouts and seven walks.