Cleveland placed the veteran designated hitter on the 15-day disabled list with lower back inflammation on Thursday and recalled infielder Jason Donald from Triple-A Columbus to assume his spot on the roster.
"There's not a specific timeframe at this point," said general manager Chris Antonetti, when asked how much time Hafner might miss.
Manager Manny Acta added that head athletic trainer Lonnie Soloff would discuss Hafner's injury in more detail on Friday.
Hafner's placement on the DL is retroactive to Monday. He last played Sunday, when he hit a home run and tallied three RBIs in Cleveland's 10-8 loss to Detroit. He sat out all three of the Indians' contests against the Twins this past week and had an MRI on his lower back on Wednesday.
The 35-year-old's back first flared up during a July 31 game against Kansas City. Hafner went on paternity leave on Aug. 1, when he and his wife welcomed the birth of their son, Trip. He returned to the ballclub on Saturday, but he sat out that night's tilt with the Tigers because of back stiffness.
It's the second stint on the DL for Hafner this season. He was sidelined for nearly six weeks after undergoing right knee surgery on May 31. In 60 games this season, he is batting .239 with 11 home runs and 32 RBIs.
Donald, who was on the club's Opening Day roster, has hit .188 (9-for-48) in 18 games for Cleveland. The utility player batted .277 with six homers and 31 RBIs in 65 contests for the Clippers.
"Donald is going to get some playing time at third base," Acta said. "He could also move over to second and occasionally in the outfield, if we need him. Right now, with [Jose] Lopez not being here, he'll probably get most of his at-bats playing third."