The surprise move was announced Thursday The 6-foot-5 right-hander yielded six earned runs and eight hits over four innings of an 11-3 loss to Baltimore Sunday.
Patterson, 30, was trying to re-establish himself after battling arm injuries the past two seasons.
The team's former ace had been mentioned recently as one of three possible choices to be the Nationals' Opening Day starter against Atlanta when it begins play at its new ballpark, Nationals Stadium, on March 30.
"Obviously, we thought we could get him back to where he was three years ago, and it never happened," General Manager Jim Bowden said on the Nationals' Web site.
"They told me I didn't blow the doors open and that there were other pitchers pitching better," Patterson said.
Over nine innings this spring, Patterson was 0-2 with an ERA of 7.00.
His best fastball was clocked in the low to mid-80s.