"I feel good. I feel fine," Alonso said. "It doesn't really hurt right now, but when it happened, it was a little flare-up and they didn't want it to get any worse."
Alonso said his left leg stuck in the ground while he was swinging through a pitch in the fifth.
"That plate has that black mud [around] it, so it's a little sticky, and I like to dig in," Alonso said. "I don't think it's anything major, anything serious, but at that point, I was feeling it a little bit on defense. They noticed, and they wanted to see what was going on. At that point, they were being more cautious than anything."
Alonso leads the A's in home runs, already belting a career-high 12 long balls.
"We'll see how he is tomorrow," manager Bob Melvin said. "Hopefully it's minor, but we'll see."
Jane Lee has covered the A's for MLB.com since 2010.