Ensberg, who pinch-hit in the ninth inning, said he didn't know how he hurt the ankle, but chances are he twisted it while running the bases during Monday's game in Philadelphia.
"I have no idea where I did it," he said. "It's kind of a tweak of the ankle and obviously you saw me pinch-hit, so it's not something that's so bad."
Ensberg said he felt the pain Monday on the flight to Pittsburgh. When he arrived to PNC Park on Tuesday, he headed for the training room and taped the ankle, but when he warmed up during batting practice, he realized the pain was worse than what he had originally thought.
"I just kind of realized that I couldn't put as much pressure [on it] as I'd like," Ensberg said. "Especially when you're throwing the ball. You're landing pretty hard on your left leg. I came up [to the clubhouse], iced it, heated it, iced it."
"I didn't know about it until batting practice," manager Phil Garner said. "He didn't know it until batting practice, either. He thought it actually was going to be OK. Then, when he got out there and started trying to move around, he couldn't move around."
Ensberg, who popped out in his pinch-hit appearance on Tuesday to end a 10-game hitting streak, left a 1 percent chance open that he wouldn't play on Wednesday, but he said he would be "shocked" if he wasn't in the lineup for the middle game of the Pirates series.
"If I couldn't do it, I wouldn't be pinch-hitting," he said.
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.