"I rolled the inside of my ankle," he said. "Right before I was about to touch the bag to check the runner at third base, I slightly rolled."
It's early enough in camp where missing a bullpen session or two won't be a big setback for Ambriz, who was 1-1 with a 4.19 ERA in 18 games after being signed by the Astros in June.
"That's frustrating for me because I came in here with my arm in good shape, and I don't want to miss many days," he said. "Hopefully, I can play catch tomorrow or the next day. If I get the swelling [down], I'll be ready to go."