Jordan Ridley will be sidelined for up to three months after it was revealed he had a stress fracture in his back.
The defender experienced discomfort during training last week, prompting the Bombers to investigate.
"Jordan has a partial stress fracture in his back, which in one sense gives us a chance to let it heal because it hasn’t broken through, so we’re going to take that opportunity," Essendon high performance manager Justin Crowe said.
"He’s going to have six to eight weeks off running and then build back up into the season.
"The good news for Jordan is he really only needs to avoid impact – which means running … so he’ll be able to do a lot of weights over the next couple of months."