Feltner (back) struck out two over 1.2 scoreless innings in a rehab start with the rookie-level Arizona Complex League Rockies on Monday.
It was Feltner's first outing in seven weeks, as he has been shelved since late April with back spasms. The right-hander will be eligible for activation from the 60-day injured list June 28, but he might need more time than that to rebuild his stamina.