Lobstein was sent back to Triple-A Indianapolis on Saturday, Rob Biertempfel of the PIttsburgh Tribune reports.
The Pirates reinstated Tony Watson from the paternity list Saturday, so Lobstein will return to Triple-A to free up a spot on the 25-man roster. The left-hander has appeared in 10 games for Pittsburgh on the season, posting a 4.79 ERA across 20.2 cumulative innings.