Olsen hurt the shoulder Saturday when he pitched five innings against the Phillies at Nationals Park.
Olsen knew ahead of time he couldn't have a short outing because the Nationals had used the entire bullpen Friday. Olsen pitched five innings, but he had a tough time getting people out.
Early in the game, in fact, Washington manager Manny Acta went to the mound to see if Olsen was OK. Acta noticed that Olsen's fastball was being clocked in the low-80s. When he's healthy, Olsen's fastball typically hits 89 mph. Olsen told Acta he was OK, but that turned out not to be the case.
Acta announced after the game that Olsen had hurt his left shoulder and was still bothered by the left ankle problems he suffered last Sunday against the Diamondbacks.
"The doctor gave him a shot," Acta said. "He is not going to throw for five days. Then he is going to start working it up again. He is going to be DL'd. We were not anticipating things to go this way."
Because of the off-day this Thursday and Saturday's doubleheader against the Phillies, the Nationals will need an extra pitcher to start on Monday against the Pirates.
Detwiler will likely make the start for Washington. He is currently with Harrisburg and was scheduled to start against Reading on Saturday, but he was scratched from that outing.
Detwiler, the Nationals' No. 1 pick in the 2007 First-Year Player Draft, is having the best season of his professional career. He is 0-3 with a 2.96 ERA. Even more impressive is the fact that Detwiler has 28 strikeouts over 27 1/3 innings and opponents are hitting just .257 against him.
Detwiler made his Major League debut a few months after he was drafted, pitching one scoreless inning against the Braves -- striking out Willie Harris in the contest.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.