Manuel said that Howard first complained about the groin in the middle of Thursday's 4-3 loss to the Cardinals. Howard was lifted in the eighth inning for a pinch-runner.
Howard had started the first 16 games and was batting .274 with one home run, five RBIs, and just a .690 on-base-plus-slugging percentage.
Against lefthanded pitching, he entered Friday batting .067 (1 for 15) with eight strikeouts, a double, one RBI, and a .125 OPS.
Ruiz X-rays negative
Phillies catcher Carlos Ruiz was hit in the left wrist with a pitch on Friday in an extended spring training game. The team said that X-rays were negative.
Ruiz, who was suspended for the first 25 games for Adderall use, is eligible to return April 28, barring any rainouts.
Brown out again
For the second straight game, Freddy Galvis started in left field for Domonic Brown, who suffered a back strain in Wednesday's 11-2 loss at Cincinnati. Brown did pinch-hit for Cole Hamels in Thursday's loss and grounded into a fielder's choice.
"Brown should be able to play [Saturday]," Manuel said. "We want to make sure his back is OK and that he doesn't have to miss a lot of time."
Galvis entered the game hitting .350 (7 for 20), so it was easy to make the decision on Brown.
Frandsen at first
Kevin Frandsen replaced Howard at first base in the starting lineup.
"I feel good there," Frandsen said before the game.
Entering Friday, Frandsen had played just five major-league games at first, starting four games for the Los Angeles Angels in 2010. He played 11/3 innings at first base in the Phillies' 2-1 loss at Miami last Saturday.
Contact Marc Narducci at firstname.lastname@example.org. Follow @sjnard on Twitter.