Lyles (hamstring) tossed a four-inning simulated game Tuesday, Adam Berry of MLB.com reports.
Rather than sending Lyles out on a rehab assignment, the Pirates elected to keep the right-hander on hand in Pittsburgh to test out his tight left hamstring in front of the team's medical staff. Manager Clint Hurdle said afterward that Lyles' next step is "to be determined," but if his hamstring responds well to the simulated-game action, he could return from the 10-day injured list to rejoin the rotation as soon as Sunday against the Padres. Steven Brault and Mitch Keller are the other candidates to take the hill that day if Lyles needs more time to recover from the injury.