Medica remained on his feet and was even seen smiling while being attended to by Padres head trainer Todd Hutcheson.
He left the game as a precaution, and pitcher Jesse Hahn replaced him as a pinch-runner with the team leading, 2-1.
"He's doing well … I think we caught a break there," said Padres manager Bud Black after the game. "He was evaluated by the Pittsburgh team doctor and he checked out fine. They're going to keep him here [PNC Park] for a while tonight, but the early signs are he's fine and he'll be able to go back to the hotel."
Yonder Alonso, who didn't start the game, replaced Medica at first base in the bottom of the inning.
Medica entered the game hitting .275 and was 0-for-2 with a run scored. He was hit in the foot by a pitch in the first inning when the Padres scored two runs.
Medica spoke with reporters after the game.
"I'm a little light-headed but it could have been a lot worse," Medica said. "It's one of those things where they said that symptoms can still happen in a few days."
Medica said the pitch cracked the back of his helmet.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.