Bryan Stow's family says he has suffered a large blood clot in his thigh and pelvis that could have been fatal.
On a note posted on their website, the family says a filter was inserted in Stow's abdomen to catch any new clots before they reached his lungs.
Stow also received injections to help dissolve the clot and prevent others.
The paramedic from Santa Cruz suffered brain damage and was permanently disabled after the 2011 beating.
Stow's family said he would be in the hospital at least through the weekend.