"I felt some tightness in my swing and then it continued to get tight in the outfield," Kotsay said. "We will have a better idea tomorrow."
Kotsay, hitting second in the lineup, flew out to the warning track in left field in the first inning and then played on defense in the bottom of the inning. He made the first out of the inning catching a fly ball off the bat of Jimmy Rollins.
When the second inning rolled around, James Darnell had taken Kotsay's place in left field for a game the Padres went on to win, 2-1.
"Kotsay has a history of some back problems but hopefully we got him out of there before it went into spasms," Padres manager Bud Black said. "Let's hope he's going to be fine."
Kotsay had back surgery in 2009 and previous stints on the disabled list in 2008 (back soreness) and in 2007 (back spasms). He also spent time on the disabled list in 2007 with a herniated disc and in 2003, during his first stint with the Padres, he missed time with a protruding disc in his back.
Kotsay opened the season on the disabled list with a strained right calf. He missed the first 10 games of the regular season with the injury.
In his first 34 at-bats with the team this season, Kotsay is hitting .294 with one home run and six RBIs.