Gonzalez instead will oppose Roberto Hernandez as these teams complete this three-game series Sunday in Philadelphia.
Hamels was expected to start this contest, but he's been pushed back to Tuesday against Toronto due to the flu. Hernandez (1-1, 5.74 ERA), who was skipped in the rotation last week and was expected to start against the Blue Jays, pitched one-third of an inning of relief in Tuesday's 6-1 loss to the New York Mets.
Manager Ryne Sandberg didn't use Hernandez out of the bullpen Friday in case Hamels' condition didn't improve.
"He's prepped to go," Sandberg told the team's official website. "We wanted to see how (Hamels) was (feeling Saturday), but we stayed away from (Hernandez) last night. He's all good to go."
The right-hander allowed four runs in six innings in his last start April 25, falling 5-4 to Arizona. Hernandez had one of the best starts of his career the last time he faced the Nationals, allowing three hits and going the distance in a 7-1 win June 12, 2010, while with Cleveland.
He'll try to match Gonzalez (3-1, 3.25), who overcame shoulder soreness after his previous outing to allow three runs and strike out a season-best nine through six innings of Washington's come-from-behind, 4-3 win over Houston on Tuesday.
The Nationals (17-13) have won five of Gonzalez's six starts with the left-hander allowing two runs or fewer four times. He's 5-2 with a 2.66 ERA in eight career starts against the Phillies, giving up three earned runs or fewer in each of his six outings at Citizens Bank Park.
Ryan Howard is 0 for 8 with four strikeouts against Gonzalez, but he hit a three-run homer in Saturday's 7-2 victory as the Phillies (14-14) snapped Washington's three-game winning streak.
Howard, who had been limited to 151 games over the last two seasons because of injuries, has at least one hit in 10 of his last 12.
''It's still kind of a game of catch-up for me," Howard said. "Just trying to take it day by day, continue to try to progress and take it as it comes.''
Cody Asche hit a solo shot and Marlon Byrd went 2 for 4 with two RBIs for Philadelphia, which had lost the last three home meetings with Washington.
''Good offense up and down the lineup, good starting pitching and good bullpen,'' Sandberg said. ''Real good combination.''
The Nationals were held to fewer than four runs for just the second time in their last seven, and their four hits marked their fewest over their last nine. Adam LaRoche went 2 for 2 with a homer and a walk, while Zach Walters hit a pinch-hit home run in the seventh.
LaRoche, who has driven in at least one run in eight of his last nine, has been battling a quad injury and was removed immediately after homering in the sixth. His status for this contest is unclear.
''We've been coming back a lot, but over the course of a season, you can't expect to keep doing it,'' manager Matt Williams said.
The Nationals had won eight of 10 meetings with Philadelphia prior to Saturday.