The center fielder opened the bottom of the first inning on Wednesday with a walk off New York's Chris Schwinden to extend his streak of getting on base safely to open a season to 24 games.
Schafer, who bruised his ribs on a catch at the outfield wall in Cincinnati over the weekend, sustained the strained oblique on Monday diving back to first base.
"It's not really my oblique, it's more my hip pointer," said Schafer. "My left side is a little tight and it bothers me.
"They wanted to give me a day to relax a bit. I'm more sore today than yesterday."
Schafer's on-base streak to start a season is one shy of the club-record of 25 set by Denis Menke in 1969.
"I'm taking it in stride -- and whenever it ends, I'll talk about it," said Schafer. "But now, I'm just trying to get on base."
Schafer left the game prior to the top of the fifth inning when his lower back tightened up.