Hill reinjured his groin during a bullpen session ahead of Wednesday's game in Milwaukee. He had an MRI on Thursday.
The 36-year-old was scheduled to throw 35 pitches during the workout at Miller Park, but he felt a "grabbing, pulling sensation" on his 33rd and 34th pitches, according to the San Francisco Chronicle.
''It was going great until the last couple of pitches, but then I felt it pull again,'' Hill said, according to the San Jose Mercury News, comparing the severity to that of the original groin strain he suffered May 29 at O.co Coliseum.
Hill leads the Oakland staff with an 8-3 record and 2.25 ERA in 11 starts. He was named the American League pitcher of the month for May.
The DL move is retroactive to May 30.
Information from The Associated Press was used in this report.