Venable said he suffered the injury during his first at-bat, a ground-ball out to second base to start the first inning.
"I took my swing and slipped out of the box a little," Venable said. "It was a ground ball so I was running hard. I was thinking infield hit and I just tweaked it a little bit."
He was replaced in center field by Chris Denorfia.
San Diego manager Bud Black said that Venable would come to Petco Park sometime Monday -- which is an off-day for the team -- to be re-evaluated and receive treatment. No determination has been made as to whether Venable will head to the disabled list.
"We will see how it sets up," Black said. "Some [oblique strains] are nasty, some are not. Some go away quickly."
Last season, catcher Nick Hundley missed 31 games with an oblique injury. Relief pitcher Luke Gregerson missed 25 games with a similar injury.
"It doesn't feel good," Venable said after the game. "It got progressively worse with everything that I tried to do."
The Padres currently have 11 players on the disabled list.