The 23-year-old Bastardo, who had posted a 6.75 ERA in five starts, is to meet with team doctor Michael Ciccotti in Philadelphia on Monday.
Phillies ace Cole Hamels will pitch Wednesday, while Thursday's starter has yet to be announced by the club. Hamels, who suffered his fourth defeat in Friday's 6-1 loss to Toronto on Friday, will be pitching on regular rest because of Monday's off-day.
Bastardo exited Thursday's start -- a 10-4 loss to the Rays -- in the fourth inning with the shoulder injury. Bastardo's velocity was clearly affected in the outing and said he felt some tightness in his shoulder recently, although he described no pain.
While it's not yet known who will start Thursday for the Phils, one possible option would be to promote prospect Carlos Carrasco from Triple-A Lehigh Valley. The right-hander is 4-7 with a 4.92 ERA. In 86 innings, he has struck out 84.
Other possible options include Triple-A right-hander Kyle Kendrick (4-4, 3.97 ERA) and Double-A righty Kyle Drabek (4-0, 2.43 ERA).
David Singh is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.