The Padres placed Estrada on the 15-day injured list Friday, retroactive to Wednesday, with right knee inflammation.
Estrada gave up a run and took the loss during his last appearance Tuesday, and he seems to have come away from the outing with a knee issue. Manager Craig Stammen said Friday that he doesn't expect the right-hander's injury to linger, per AJ Cassavell of MLB.com, so he could be cleared to return when first eligible. In the meantime, David Morgan will come up from Triple-A El Paso to round out San Diego's bullpen.