The Washington Nationals placed ace Stephen Strasburg on the 15-day DL on Wednesday after he was unable to make a scheduled bullpen session, according to ESPN. "There's still some tenderness and discomfort there," manager Davey Johnson said. "So we're going to keep him off the mound for a few more days."

Strasburg was removed after two innings during his last start on Friday against the Atlanta Braves. He was seen grimacing and flexing his shoulder during the appearance and said after the game that his back had been bothering him while warming up for his previous few starts but would feel fine once the game started.

The Nationals said on Sunday that Strasburg has a "slight strain" to the lat muscle. Johnson was hoping his top pitcher would not miss a start although Strasburg's next turn in the rotation was moved back to days to Saturday.

After participating in a game of catch instead of throwing the bullpen session on Wednesday, the team decided to put Strasburg on the DL, retroactive to Sunday.

Strasburg is 3-5 with a 2.54 ERA. He was 15-6 with a 3.16 ERA last season as the Nationals decided to place him on a pitch count and shut him down before the playoffs after his first full season following elbow surgery.

Washington now has two starters on the disabled list. Ross Detwiler has been sidelined since May 15 with a strained oblique muscle. He threw a bullpen session Wednesday and will make a rehab start in the minors before returning to the rotation.