"He took it to another level, and we'll see him Tuesday," manager Bob Melvin said. "Everything's going well to this point."
So far, the A's have been keeping Anderson in the 30-pitch range during multiple sessions, remaining extra cautious with their Opening Day starter, who hasn't pitched in a game since April because of a stress fracture in his foot.
"We're trying to take him through a process where we can keep him healthy and not push him too much," Melvin said. "Not only are you trying to make sure the foot's no longer an issue, you're also trying to incrementally make sure the arm's not getting pushed as well."
If the A's need pitching help sooner rather than later, they may be inclined to bring back Anderson as a reliever. The lefty has stated that he would welcome any role, so long as he's back on a big league mound.
"I think anything is an option at this point. We'll see what our needs are, and we'll see how far we can speed him along," said Melvin.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.