Lyles is set to throw 45 pitches Monday in his first bullpen session since fracturing the middle metacarpal on his left hand June 4. If all goes well, he's scheduled for a live, 30-pitch batting practice session on Friday.
Chatwood is set to throw live batting practice Wednesday for the first time since experiencing tightness in his right forearm in his previous live batting practice session last Wednesday. His pitch count for that next step has yet to be decided.
Brett Anderson (fractured left index finger) remains likely to return shortly after the All-Star break as he progresses on his rehab assignment as well. This flush of good news had manager Walt Weiss optimistic for the second half considering he's been scrambling for starting options since the calendar flipped to June.
"It looks like we're starting to get multiple guys back at the same time," Weiss said. "They're not coming back at exactly the same time but they're trickling in here. It will be good to get everybody back."
Christian Bergman (left fractured trapezium) will also participate in a live batting practice session with Butler on Tuesday. But he is ineligible to return from the disabled list until Aug. 20.
Cody Ulm is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.