The news came after the Nationals defeated the Cardinals, 4-3, at Nationals Park on Sunday afternoon.
Strasburg threw six shutout innings in Washington's victory, allowed two hits and struck out nine to raise his total to a National League-leading 195 in 156 1/3 innings. After having Tommy John surgery in late 2010 and coming back late last year, Strasburg is on an innings limit in '12. He is expected to pitch between 160 to 180 innings this year.
The plan to shut down Strasburg has been in place since last year. The team had a similar plan for Jordan Zimmermann last year, and he's developed into one of the club's best pitchers.
"We had parameters in place at the beginning of the season," general manager Mike Rizzo said. "We have our philosophies, protocols and that seemed like the right number of innings to end the season in. When we feel he has had enough -- stressful innings, pitches and that type of thing -- we'll make that decision and shut him down."
Johnson said the team has faced adversity all year because of injuries and will survive without Strasburg.
"I think two starts [for Strasburg]. Unless I let him pitch 10 [innings] the next one out, which I'm not going to. So I think his last start will be on the 12th," Johnson said. "We've faced adversity all year long. I mean, we didn't have our cleanup hitter [Michael Morse], we didn't have our closer [Drew Storen]. We lost our starting catcher [Wilson Ramos], we lost Jayson Werth for two months.
"I mean, that's the way this year has been. We've been fortunate in the starting staff, with the exception of Chien-Ming [Wang] early on pulling his hamstring, everybody on the pitching staff has been very healthy. We've been through it."
Strasburg said he has yet to have a conversation with Johnson or Rizzo about the rest of the season.
"No, I'm just focused on the next start. That's all I can really focus on right now. But we're going to have to have a sit-down and talk here soon," Strasburg said.
Rizzo said he knows that Strasburg will be upset over the decision.
"I don't think he is going to fight me on it," Rizzo said. "I know he will be unhappy about it. He is an ultra competitor. We have taken that out of his hands. This is a developmental decision and it ultimately falls on the doorstep on the general manager, and we made it five months ago and we are going to stick to it. ...
"The plan was in place. It couldn't have gone any better. He has pitched extremely well. A couple of more starts under his belt, it will lay a solid foundation for 2013, where he can take the ball, run with it and win a lot of games for us."
The Nationals will likely stick with a four-man rotation should they reach the postseason. There is no need to have five starters in a short series in October.
"I think we have four of the top pitchers in the National League," Rizzo said. "I think all of them can go out there under a playoff atmosphere. I think they are ultra-talented and they are stuff guys, and I think they are going to be tough to deal with against any team we play against."
Outfielder Jayson Werth said it doesn't come as a surprise that the team will shut down the talented young righty and agrees with management's decision on Strasburg's development.
"I've known this is the way it has been since last year," Werth said. "I have no reaction. This has gone on all season. People have been talking about it this for the whole year. I don't know why everyone is so surprised.
"This has been the protocol for two years now. It's real easy for people not in the organization and not on this team to point fingers and call people names and say this is what should happen or what shouldn't happen. But the bottom line is, this is our guy on our team. And [the Nationals] are doing what's right for him, what right for our club long term. I think it's great."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.