"I thought things were going well," the right-hander said in a telephone interview from Florida.
Patterson was Washington's opening-day starter in 2007. But he missed much of the last two seasons because of right forearm problems, limiting him to 15 starts in 2006 and 2007 combined. He had surgery in September to repair a nerve problem.
Still, he was considered in contention to get the start against the Atlanta Braves on March 30, when the Nationals begin this season at their new ballpark.
"We spent spring training evaluating him, and we came to the conclusion it was better to give our younger kids a chance to start," Nationals manager Manny Acta said by telephone from the team's camp in Viera, Fla.
"It's a rehabilitation-in-progress," Acta added, "and we can't afford to do that every five days."
In other moves Thursday, the Nationals purchased the contract of left-hander Odalis Perez, and put right-hander Shawn Hill (right forearm), outfielder Wily Mo Pena (left side muscle) and reliever Ryan Wagner (right shoulder) on the 15-day disabled list.
The team also reassigned second baseman Bret Boone to minor league camp, saying he would begin the season at Triple-A Columbus. Boone, who turns 39 next month, came out of retirement to sign a minor league deal with the Nationals in February. He hasn't played in the majors since 2005.
Patterson was called into general manager Jim Bowden's office Thursday afternoon to get the news.
"I knew that it was possible, but it was a little bit of a surprise," the pitcher said. "They didn't feel like I was 100 percent yet."
He, on the other hand, said his arm feels OK.
"I don't have any pain," Patterson said. "I've been able to throw every day."
The 30-year-old Patterson hasn't been able to recapture the form he showed for Washington in 2005, when he was 9-7 with a 3.13 ERA and 185 strikeouts in 198 1/3 innings.
In his final exhibition start for the Nationals, last Sunday against the Orioles, he allowed six runs and eight hits in four innings.
"What we did is best for both the team and John. It gives him enough time to get a job somewhere else," Acta said. "It would have been worse to keep him to the end."
Hill is another pitcher coming off surgery who at the beginning of spring training was thought to be in the running for the opening-day start.
And it leaves Patterson looking to catch on with another major league club.
He spent several hours on the phone Thursday, speaking to his agent and getting a sense of what team might be a good fit.
"I've never been released before, so I was wondering, 'What's the next step? What do I do now?" Patterson said. "We're talking with some teams, waiting to see what will happen. We're waiting to see what offers are out there."