Before the three-game series against the Cubs, the Phillies fired hitting coach John Mallee and hired former World Series-winning manager Charlie Manuel to replace him.
"I'm excited about it," the 75-year-old Manuel told reporters. "I think it's a challenge, and I like that. I've never been scared of anything like that, especially when it comes to hitting. It's one of my favorite things to talk about. I'm looking forward to it."
Harper has three home runs in his last two games and 25 this season.
The Phillies will send right-hander Vince Velasquez (4-7, 4.30 ERA) to the mound to try to extend their winning streak.
Velasquez is 2-4 with a 4.50 ERA in nine starts since returning from the bullpen back to the starting rotation.
In Velasquez's last start on Saturday, he gave up three hits and three runs in five innings in a 3-1 loss at San Francisco. Two of the hits were home runs to Evan Longoria and Kevin Pillar.
"It was one of those days where you're kind of dealing with adversity and you're trying to find something that works," Velasquez told reporters. "You're going to have outings like this where things are not going to go your way. You're not going to feel great. You're not going to have a lot of life on your fastball. It's a matter of finding ways of getting outs."
The Padres are expected to be without potential Rookie of the Year candidate shortstop Fernando Tatis Jr. Tatis has been struggling with a sore back and is likely to land on the injured list.
Tatis is hitting .317 with 22 home runs, 53 RBIs and 16 stolen bases.
"Sometimes with backs, you just don't know," Padres manager Andy Green told reporters. "You're always just crossing your fingers (and) hoping. He's obviously been a huge part of everything we've done this year."
San Diego will send 23-year-old Chris Paddack to the mound for his 21st start of the season. Paddack is 7-5 with a 3.26 ERA.
Last Saturday, Paddack tossed six innings and gave up five hits and three runs in an 8-5 win over the Colorado Rockies.
"I still felt like it wasn't my best," Paddack told reporters. "I'm never going to really settle for being all right when I know that I could've done a little better job of making some pitches."
The Padres are 27-31 on the road and will be searching for their second straight win overall.
Third baseman Manny Machado, who was coveted as a free agent by numerous teams including the Phillies, will enter this series with a .263 average, 26 home runs and 70 RBIs.
--Field Level Media