Zito has been on the disabled list since Aug. 1 with a right foot injury and may have aggravated that injury. Zito twisted his right leg while coming off the mound to field his position.
"He either stepped on the bag wrong or the grass wrong," Giants vice president Bobby Evans told Andrew Baggarly of the San Jose Mercury News. "I have to believe it's the same foot. Any time a guy is helped off the field, especially with an injury he's had before, it's not good."
The 33-year-old is 3-4 with a 5.62 ERA in nine starts this season.For more baseball news, rumors and analysis, follow @eyeonbaseball on Twitter or subscribe to the RSS feed.