The team said Reddish will wear a walking boot on his right foot and be re-evaluated in one week.
The second-year forward has struggled throughout his first two NBA seasons, averaging 10.7 points and 3.8 rebounds on 37.8 percent shooting. While there were signs that Reddish had work to do during his lone season at Duke, his performance level has been a disappointment.
The poor play was exacerbated by the Achilles injury, which has already cost him six games, and the Hawks have been one of the NBA's biggest disappointments after an offseason signing splurge.
The All-Star break could limit how much time Reddish misses, but the one-week timeline would take him out for at least the next three contests. His absence will continue to leave the Hawks shorthanded on the wing.