Franco is hitless in his last 15 at-bats and is 1-for-17 (.059) in his last five games. He is 2-for-34 (.059) against Washington this year with three RBIs in nine games.
"I'm not saying he is going backwards," Phillies manager Pete Mackanin said Friday, sitting in his office at Nationals Park. "He is at a stalemate right now (at the plate)."
The Phillies and Nationals will play as scheduled on Saturday, with Washington right-hander Tanner Roark (3-1, 3.46 ERA) facing Phillies right-hander and former Washington minor-leaguer Nick Pivetta (0-2, 5.40 ERA). Both pitchers were slated to start Friday.
Roark is 5-5 with a 3.21 ERA in 14 games, including 12 starts, in his career against the Phillies.
Pivetta gave up three homers to the Nationals on May 5 in a loss at home in his second start at the major league level. He gave up four runs in five innings in that game.
The Friday rainout will be made up as part of a day-night doubleheader on Sunday, with the first game at 1:35 p.m. and the second game at 7:05 p.m.
Philadelphia's Vince Velasquez (2-3, 5.94 ERA) will face Washington's Max Scherzer (4-2, 2.59 ERA) in the Sunday night game. Washington is 22-12 and began Friday 5 1/2 games ahead of the New York Mets, while the Phillies (13-19) started the day eight games back.
It was the second day in a row the Nationals were rained out, after their home game with Baltimore on Thursday was pushed back until June 8.
"You have to keep mentally prepared to play," Washington catcher Matt Wieters said Friday. "Our schedule is packed as it is; you want to play anytime you can. You are already here at the park. But there is no reason to get frustrated."
Franco will try to get back on track against the Nationals on Saturday. Franco has certainly shown he can adjust to major league pitchers.
Franco, 24, broke into the majors with the Phillies in 2014 and hit .179 in 16 games.
He played in 80 games and hit .280 in 304 at-bats with 14 homers and 50 RBIs in 2015 with the Phillies. Last year he played in 152 games and hit .255 with 23 doubles, one triple, 25 homers and 88 RBIs.
Franco has proven to be a run-producer already this season for Mackanin, who signed a contract extension with the Phillies on Thursday.
He became the first Phillies player to hit two grand slams before the end of April. He entered Friday ranked first in the National League with two grand slams and was tied for fourth in go-ahead RBIs with eight.
"You have to be able to change drastically your approach (when pitchers adjust). At some point he is going to get it," Mackanin said of Franco.
NOTES: Phillies manager Pete Mackanin signed a contract extension Thursday. Mackanin was drafted out of a Chicago high school by the Washington Senators in the fourth round in 1969 ... Washington 1B Ryan Zimmerman became just the fourth player in major league history to hit 13 homers and bat .400 in the first 30 games of his team's season. The others were Mickey Mantle (1956), Willie Mays (1964) and Josh Hamilton (2012) ... Washington hitting coach Rick Schu played for the Phillies from 1984-87. The Nationals entered Friday leading the majors in several categories, including batting average and runs scored.