The Brazil president's office announced on Sunday, Xinhua news agency reported.
The bloc is holding its 16th summit from October 22 to 24 in Kazan.
Lula da Silva, 78, "will not be travelling to the BRICS Summit" due to medical advice to avoid long-haul flights, his office said in a release.
The president, however, will be participating in the summit via video conference from Brasilia, where he will carry out his usual work schedule next week, it said.
Lula da Silva was admitted to a hospital in Brasilia with a "bruise" on the occipital region of the head.
"After an evaluation by the medical team, Lula was advised to avoid long-haul air travel but be able to carry out all other activities," according to a statement signed by doctors.
Last year, Lula da Silva, who will turn 79 on October 27, underwent hip surgery.
The Brazilian government said in a post on X that Foreign Minister Mauro Vieira has been designated to lead the delegation at the BRICS summit. The delegation departed on Sunday.