Pat Sullivan / AP

Nationals reliever Sean Burnett will undergo surgery next week to remove a small bone spur or two in his left elbow after he pitched with symptoms for the second half of the season, according to a person familiar with Burnett’s injury.

Burnett, 30, served as a reliable left-handed setup man this year, posting a 2.38 ERA over 56 2/3 innings with two saves. Burnett felt no significant discomfort in his elbow until shortly after the all-star break, and the Nationals did not confirm that he had the bone spurs were the source of the soreness until the final week of the season. The procedure is relatively simple and will likely not even affect Burnett’s offseason throwing program.

Burnett appeared in two games in the Nationals loss to the Cardinals in the NLDS, knowing he was pitching with the bone spur in his elbow. He allowed three runs in less than an inning in Game 2. He usually throws his sinker about 92 mph, and last night he retired lefty pinch-hitter Skip Schumaker, the only batter he faced, throwing 87 and 88 for a key out the sixth.

Burnett, a key piece of the Nationals’ bullpen for the past three seasons, also pitched through the injury knowing he will likely become a free agent this offseason. After he completed a two-year contract that carried him to his first year of free agency, he and the Nationals hold a mutual option for next season worth $3.5 million.

While Burnett would like to stay in Washington, he seems likely to decline the option even if the Nationals wanted to exercise it. Left-handed relievers of his ability tend to make more on the open market. As an example, Jeremy Affeldt of the San Francisco Giants made $5 million this year as he punched up a 2.70 ERA in 63 1/3 innings.

The Nationals and Burnett briefly discussed a contract during the season that would keep Burnett in Washington for more than one season, and those talks could reopen. The Nationals have until five days after the World Series ends until Burnett becomes a free agent, assuming he declines his options.

But first, Burnett will have surgery to and recover from the injury he pitched through for half a season. Early in his career, Burnett underwent Tommy John surgery and a shoulder operation, two procedures that essentially turned him from a starter to a reliever. Burnett is now one of the most well-liked members of the Nationals’ pitching, and his painful performance in the second will engender more respect for him.