The Washington Nationals optioned struggling rookie third baseman Carter Kieboom to their alternate site in Fredericksburg, Virginia, and reinstated closer Sean Doolittle from the injured list on Wednesday.

Doolittle had gone on the IL on Aug. 13, retroactive to Aug. 11, because of right knee fatigue. Doolittle has been ineffective for most of the season, racking up a 15.00 ERA.

Kieboom, 24, was anointed the starter at third base with the departure of Anthony Rendon in free agency. The 2016 first-round pick started out well but has faltered recently. He was batting .200, and the frustration was showing. He slammed down his helmet after grounding into a double play on Tuesday night, and shouted in the dugout after hitting into another double play.

Asdrubal Cabrera is expected to take over as the regular third baseman.