Charlie Morton will likely take Vance Worley's rotation spot when he returns. Worley is now in the bullpen. Morton's last rehab start is scheduled for Tuesday, and the Pirates have two days off this coming week, so Worley won't be needed by the time Morton returns.
The Pirates' preference for Locke over Worley is no surprise, given that they also picked Locke over Worley at the end of Spring Training. Neither of them have done much to justify the stumping people did for each of them back then, but Locke probably actually has been the better of the two, despite a wretched ERA -- he's recorded strikeouts at a higher rate and walks at a lower rate, and he has more ground balls. The big difference between them has been that Locke has allowed five homers while Worley has allowed two.
Also, Jordy Mercer is out of the Pirates' lineup today. The Bucs told Mercer before the series that he wouldn't be in their lineup this weekend. Jung-Ho Kang starts at shortstop in his place.