The Argentine was introduced to the media on Nov. 10 but returned south for a previously scheduled hospital appointment and has not yet returned.
He communicated with his backroom staff from a distance but after three 2-1 losses in three games the Rio club sacked him.
“Unfortunately, because of the coach’s health problems and his discharge scheduled for Dec. 7, the club has decided that it cannot wait any longer,” Botafogo said in a statement.
Botafogo sit second bottom of Brazil’s 20-team Serie A. They appointed Eduardo Barroca to replace Diaz.
He is their fifth coach since the season restarted in June after a three-month hiatus because of the COVID-19 pandemic.