Lee, who had previously been sidelined after breaking his wrist April 19, said the cause of the child's illness was still unknown, the Chicago Sun-Times reported Monday.
"We've had a family emergency. It has to do with our daughter," Lee said Sunday. "Until we get this cleared up, I won't be with the team.
"My daughter's lost some vision in one eye, and until we find out more at a later time ... right now we have to go through some more tests," he said. "We just ask for everyone's prayers. We need a miracle and we ask for your prayers. We need everyone to believe she's going to be OK."
"You break your wrist and you think that's a big deal," Lee said. "Then something like this happens, and it really slaps you in the face. It's all about your loved ones and your family."