Nationals first baseman Nick Johnson was placed on the 15-day disabled list Thursday with a torn tendon sheath in his right wrist.

He is expected to miss four to six weeks. Washington plans to activate first baseman Dmitri Young from the DL on Friday.

Young went on the disabled list April 8, retroactive to April 3, with a lower back sprain. He had been on a rehab assignment at Double-A Harrisburg.

Johnson was injured on a swing late in Tuesday night's game.

The oft-injured Johnson missed last season while recovering from a broken leg. He is batting .220 with five homers and 20 RBIs this year. He has walked 33 times, however, giving him a .415 on-base percentage.

Aaron Boone started at first base Thursday. He broke up Mike Pelfrey's no-hit bid with a leadoff single in the seventh inning and had two key assists in the field during Washington's 1-0 win.