The move, which became official on Wednesday, came a day after his agent, Alan Herman, said that was the most likely course of action.
"The timeline is such that it would make sense to designate him for return," Herman said Tuesday.
This move assures that Tretter, who will not need surgery on his knee fracture, will miss at least the first eight weeks of the regular season. He is eligible to begin practicing after six weeks.
The Packers cannot use the injured reserve/designated to return tag on any other player this season, so any other injured players will either have to remain on the roster or go on season-ending injured reserve.