"He was examined by a doctor, and there's still some tenderness and discomfort there," Johnson said. "We're going to keep him off the mound for a few more days and he'll come back the 15th."
After feeling lingering discomfort in multiple starts, Strasburg was lifted from his last start against the Braves after just two innings. He told pitching coach Steve McCatty that he was feeling better on Tuesday, but Johnson and general manager Mike Rizzo opted to take a more cautious approach.
"All along, we felt that this type of injury is usually a DL type of injury," Rizzo said, "but because he felt good, we wanted to see where he was at."
Added Johnson: "Any time a pitcher -- starting pitcher, anybody -- has something in the upper torso that's causing him discomfort from being able to throw, it's a concern. Not so much with that injury, but what it might do to his arm. So we just want to make sure that's out of there and he's free and loose and he can go and get on the mound and do his work and then go start a game."
Strasburg was in line to start Saturday against the Twins, a slot that Johnson said will now be filled by a callup from Triple-A Syracuse. He would not name the player, but said that he had "a pretty good idea" of who would make the start. Among the top candidates are left-hander Danny Rosenbaum and right-hander Ross Ohlendorf.
Rosenbaum last pitched on Monday and is scheduled to make his next start Saturday, which would align nicely for a Major League callup. In 11 starts at Syracuse, he is 5-3 with a 3.48 ERA. He was selected in the 22nd round of the 2009 Draft out of Xavier University.
Ohlendorf last pitched on May 30 and missed his scheduled start on Tuesday, an indication that he might be the replacement. Ohlendorf, who has made 73 Major League starts, mostly with the Pirates, is 4-5 with a 4.32 ERA for Triple-A Syracuse this season.
Placing Strasburg on the disabled list freed up a spot on the Nationals' 25-man roster. Left-hander Xavier Cedeno, who was acquired on waivers from Houston in April, was recalled from Syracuse.