Hernandez is 6-8 with a 3.87 ERA in 23 games (20 starts) this season. The 33-year-old signed a one-year, $4.5 million deal with the Phillies in the offseason.
The righty was scheduled to start Thursday's series finale against the Houston Astros at Citizens Bank Park (see game notes).
The club selected the contract of right-hander Sean O’Sullivan from Triple-A Lehigh Valley to replace Hernandez on the roster, but a replacement starter has yet to be announced because O'Sullivan may not arrive on time. Cesar Jimenez will start if O'Sullivan isn't there on time. (UPDATE 5:50 p.m.: O'Sullivan will start.)
O’Sullivan is 5-9 with a 4.57 ERA in 21 starts for Lehigh Valley and made a spot start for the Phillies on June 28 -- he took the loss after allowing four runs and eight hits in 5 2/3 innings to the Braves.