Anderson has already sported the boot for a month, but the stress fracture in his right foot has not fully healed. He'll be reevaluated in another four weeks.
That's when the All-Star break begins, meaning Anderson likely won't be pitching until at least the end of August, and that's if all goes well.
This news only adds to a frustrating series of events for the southpaw, who, still just 25, has been limited to 38 starts over the last three seasons because of four stints on the disabled list.
Originally placed on the disabled list May 1, Anderson had posted a 1-4 record and 6.21 ERA in six games, five of them starts, up to that point.
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.