Barker (elbow) was designated for assignment Tuesday, Sophia Minnaert of Bally Sports Wisconsin reports.
The move clears space for the Brewers to add Trevor Rosenthal (hamstring) to the 40-man roster after he was acquired in a deadline-day deal with the Giants. Barker hasn't pitched in over a month due to a UCL sprain, and it's not yet clear when he'll be able to return to the hill.