(Luis Alvarez/Associated Press)

Strasburg will make his sixth minor league rehab start Thursday at Class AA Harrisburg. If all goes well as he throws about 75 pitches over six innings, it will also be his last minor league rehab start. The Nationals, assuming nothing goes wrong, will bring him to the majors five days later to face the Los Angeles Dodgers.

“I’ve got a spot open for him,” Johnson said, smiling.

When Strasburg returns to the majors, the Nationals will treat him with caution. Johnson plans to limit Strasburg to either four innings or 60 pitches on Sept. 6, whichever he reaches first. Johnson will likely have another starter — potentially call-up Brad Peacock — “piggyback” Strasburg, relieving him with the intention of throwing several innings.

“Kid gloves,” Johnson said. “I always err on the cautious side, especially in this case.”

Rehab from Tommy John surgery takes 12 to 18 months. Strasburg underwent Tommy John surgery Sept. 3, 2010, meaning he will return after 12 months and three days. Sept. 6 will bring the final milestone following so many — when he got his cast off last October, when he threw for the first time in January, when climbed a mound for the first time this summer.

Saturday night, Strasburg pitched five perfect innings at Class AAA Syracuse before allowing two runners to reach base in the sixth inning. In five rehab starts, spread out across three affiliates, Strasburg has allowed eight earned runs in 14 1/3 innings, striking out 25 and walking three while consistently throwing his fastball in the high-90s and his breaking ball with a sharp bit.

“It’s great,” Johnson said. “He was all worried because he was getting beat up down there in Hagerstown. I said, ‘Don’t worry about it. Just get your work in. Don’t overthrow.’ Then he had a great outing. He’s still got one more and we’ll take it from there.”

Johnson announced the Nationals’ plan for Strasburg as he answered another question, about which pitcher would replace Jordan Zimmermann in the Nationals’ rotation. (Zimmermann, incidentally, reached a 160-inning limit the Nationals prescribed because he pitched in his first full season after his own Tommy John surgery.) Johnson said Class AAA Syracuse Tom Milone would start before dropping another bit of news.

“We’ve got another young pitcher who’s coming up and will make his last start, I guess, in the minor leagues on Thursday,” Johnson said. “His name is Strasburg.”