The Twins placed Wallner on the 10-day injured list Wednesday with a left oblique strain, Bobby Nightengale of the Minneapolis Star Tribune reports.
Wallner suffered the injury during a pinch-hitting appearance in Tuesday's loss to the Marlins, and it will cost him the remainder of the regular season. He would be eligible to return during the ALDS if replacing an injured player, although neither the Twins making it that far nor Wallner being healthy by then is guaranteed. Austin Martin has rejoined the active roster in Wallner's place.