Billingsley threw fastballs, changeups and curveballs in a bullpen session.
"I'll mix in cutters next time, I'm not sure when," Billingsley said. "We'll see how the arm reacts from this."
Billingsley said he was confident he wouldn't have a problem Saturday because he had "flipped" curves while playing catch on flat ground previously.
Billingsley hasn't had a setback since starting his rehab.
"I've been very lucky," he said. "At this stage of the rehab, we're really testing it, stressing the ligament a little more, building strength into it."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.