"Unfortunately Jagger had a severe spinal injury which was not improving, and his condition was deteriorating," the post reads.
"Jagger was a very special little dog and will be greatly missed."
The post advises people who wish to make a donation towards the cost of Jagger's care to come into the clinic, or donate online to account number 02-0655-0059177-000 under Animal Care 2002 Ltd with the reference "Jagger".
"Jagger's family are very grateful for the support they have received. Any excess funds will be passed onto Jagger's owner."
Haldane, who herself was injured by a fall during the attack, said on Friday that she had kept poodles as pets all her life, and would consider getting another poodle if Jagger didn't make it.
An investigation into the attack by Hastings District Council's Animal Control was ongoing on Sunday.