Rizzo searching for depth in the bullpen

Without a doubt, the Nationals bullpen has the most questions on the team's roster this winter. General manager Mike Rizzo's decisions with his core of relievers begins with whether to forge forward or part ways with veteran right-handers Jonathan Papelbon and Drew Storen after stormy conclusions to both of their seasons.

Right-hander Casey Janssen had a nightmare of a year and the Nationals declined his 2016 option, making him a free agent. Left-hander Matt Thornton also entered free agency after posting a 2.18 ERA in 60 appearances in his first full season in Washington. FOXSports.com reports the Braves are pursuing the 39-year-old Thornton, as well as right-hander Darren O'Day, who could be a target for the Nationals if the price tag isn't too high.

David Carpenter only appeared in eight game after the Nats acquired him in a trade with the Yankees in June, but the right-hander figured to contend for a spot in the bullpen next year. Earlier this week, the Nats outrighted Carpenter to Triple-A Syracuse, so the veteran reliever opted for free agency. He signed a minor league deal with an invite to spring training with the Braves on Friday.

Right-hander Craig Stammen figures to be healthy for the start of spring training after undergoing season-ending flexor tendon surgery in April. He was missed badly last year and should add stability to the bullpen if he can fully regain his effectiveness.

Left-hander Felipe Rivero impressed in his rookie season, proving he can handle high-leverage situations. Besides his exploding high-90s heater, Rivero also showed endurance, pitching more than one inning in 14 of his 49 appearances. Hitters struggled from both sides of the plate against Rivero, with lefties managing just a .198 average and righties only .200 while he posted a 2.79 ERA.

Right-hander Blake Treinen had a rocky year in his first full season in the bullpen that included a trip back to Syracuse. But the hard-throwing 27-year-old impressed upon his return from the minors, not allowing a run in 11 appearances in August. He battled control issues at times, walking 32 in 67 2/3 innings and finishing with a 3.86 ERA.

Right-handers Abel De Los Santos and Rafael Martin and lefties Matt Grace and Sammy Solis also made their major league debuts last year, flashing at times but failing to show consistency so far.

"We need to upgrade the bullpen," Rizzo said on MLB Network on Friday. "We like Pap and Drew in the back end of the bullpen. They're both under contract and unless something happens where we get a real baseball deal to move one of them, then they're gonna be in the back end of the bullpen.

"But we still need to upgrade the bullpen. We need to get deeper. We need to have more veteran presence. We need to have a greater skill set to get out both right-handers and left-handers. We're gonna be active in that market, be it the trade market or the free agent market, because we think it's a point of emphasis for us."