Ian Krol. (Jonathan Newton / The Washington Post)

In the past week, the Nationals have traded away two left-handers from a bullpen that was already thin on them, let alone proven and reliable ones. After being designated for assignment, Fernando Abad was shipped to Oakland for a minor league outfielder. And on Monday, General Manager Mike Rizzo flipped home-grown backup infielder Steve Lombardozzi, left-handed starting prospect Robbie Ray and left-handed reliever Ian Krol, formerly a player-to-be-named-later in the Michael Morse deal, for proven right-handed starter Doug Fister.

The left-handed side of the bullpen is area that the Nationals hope to address the rest of the winter. The top four of the rotation is set, and there’s plenty of competition and depth for the fifth spot, with Ross Detwiler as the incumbent. The lineup is mostly set, based on Rizzo’s comments; the only competition at second base with second-year Anthony Rendon as the starter heading into spring training. The remaining needs for the Nationals are clear: upgrade the bullpen and the bench.

“We feel that we’d like to tweak the bullpen a little bit,” Rizzo said during Tuesday’s conference call with reporters. “We’d like to help the bench a little bit. We wanted to address the rotation, which we’ve done. We still have some work to do. Like I said, we’re not a flawless team but we think that we have a good, talented ball club and I think that going into the Winter Meetings, we like the construction of the roster and the makeup of the ball club.”

As the roster is constructed now, Xavier Cedeno would be the only returning left-hander in the bullpen. He showed promise late last season and impressed the team but in only 11 games, so projecting his impact is a gamble. If Detwiler were to lose out in the fifth starter’s competition, he could be an option in the bullpen with his fastball-heavy and limited pitch arsenal. The Nationals have could break prospect and hard-throwing left-hander Sammy Solis into the majors in the bullpen.

Rizzo said he believes the Nationals’ in-house options “can perform at a high level” but was open to upgrading the left-handed side of the bullpen through trades or free agency. They have been in touch with Boone Logan, a Yankees free agent coming off elbow surgery. They have also expressed significant interest in Oliver Perez. The Nationals were interested in J.P. Howell last year when he was a free agent and Howell is a free agent again this year after one season with the Dodgers. Other potential left-hander relief free agents include Eric O’Flaherty, Scott Downs, Matt Thornton and former National Michael Gonzalez.

“We think that’s one of the things we have to address,” Rizzo said. “We have in-house options there. I think we’re better suited going into spring training with our left-handed bullpen than we [were] last year. But it’s something that we’re looking into the free agent market or the trade market and trying to upgrade. It’s a spot that we feel that we have to upgrade at.”

In the past, the Nationals have shown restraint in pursuing pricey left-handed relievers. They were outbid by the Brewers for Tom Gorzelanny last year and just recently Javier Lopez chose the Giants’ three-year, $13-million offer, in part, because he wanted to remain in San Francisco despite being a Washington area native. Under Manager Davey Johnson, the Nationals valued left-handed relievers who were effective against both left and right-handed batters. Lopez, however, for example is a left-handed specialist. Rizzo said the type of left-hander pursued would rest somewhat on new Manager Matt Williams.

“I think it’s according to what the manager’s preference is and I think that in our division it’s important to have both a guy who can really go out and get a good left-handed hitter out, because we have a lot of good left-handed hitters not only in our division but in our league, but it’s also important for a left-handed pitcher to get out right-handed hitters, too, in our league,” Rizzo said. “So, it’s a fine balance. I think you have to put your assets and your money where you get the most bang for your buck and that’s what we’re looking to do.”

The bench could also use some tweaking. The Nationals appear open to relying on Jhonatan Solano as Wilson Ramos’ backup, but there are free agent catchers available, too, such as J.P. Arencibia, veterans John Buck, Wil Nieves and Yorvit Torrealba, among others.

If Danny Espinosa shows enough progress in spring training, he could likely join the bench as the backup to Ian Desmond and Rendon and fill Lombardozzi’s role as the switch-hitting pinch-hitter. But with right-handed hitters Scott Hairston and Tyler Moore returning, the Nationals still could use a left-handed batter, perhaps one that could also play the outfield. Left-handed outfielder Corey Brown, who has spent the most of the past four seasons at Class AAA Syracuse, could fill that void if he makes the Nationals out of spring training but there are plenty of veteran free agents, including some players released after not being tendered contracts on Monday night.