Cawarral stud owner John Brady, who said he suffers from heart disease, was taken to Princess Alexandra Hospital with stress-related symptoms.
Brady has told reporters of his concern for the welfare of those exposed to the virus, and has voiced fears over the financial impact of the outbreak on his farm operation, especially following losses from Australia's recent equine influenza outbreak.
Meanwhile, the three stud workers who were potentially exposed to the virus - Angela Webber, Adrian Daniels and Debbie Brown - have left Princess Alexandra Hospital, having spent several days there for observation. It is understood they continue to test negative for the virus.
They will report twice daily for check-ups.
Veterinarian Dr Alister Rodgers remains in hospital. The most recent report had him in intensive care in an induced coma.
Three horses at Brady's J4S Equine Nursery have died as a result of Hendra, and authorities suspect the virus was behind the earlier death of a fourth horse at the property.
The last to die was euthanized after returning a positive test for the virus.
The Queensland Horse Council has established a fund to help support the stud through its difficulties.