PHOENIX -- The Arizona Diamondbacks placed starting pitcher Ryne Nelson on the 15-day injured list with right shoulder inflammation Saturday.

Nelson's injury is a blow to a team that's in a tight battle for one of the National League wild-card spots. The right-hander has been arguably the D-backs' best pitcher over the past few months and has a 10-6 record with a 4.33 ERA.

The move is retroactive to Sept. 11, which means Nelson could return before the end of the regular season. Arizona called up left-hander Brandon Hughes to take Nelson's spot on the roster.

The Diamondbacks also announced that catcher Andrew Knizner was designated for assignment.