Ronaldo personally contacted fellow countryman Castro to convince him to take the Al Nassr job, sources said.
Thursday’s Copa Sudamericana group game against Magallanes will be Castro’s last game in charge of Botafogo.
Castro will put pen to paper on a two-year contract with Al Nassr, with an option to extend the deal for a further season.
Castro’s contract with the Rio de Janeiro based club expires at the end of the year and Al Nassr will pay Botafogo €2.3 million as part of his release clause.
The former Vitoria Guimaraes coach took the reins of Botafogo in March 2022 after temporarily managing Qatari club Al-Duhail SC.
He has guided the Alvinegro to 42 wins, 14 draws and 23 defeats in 79 games in charge.
Botafogo have enjoyed a strong start to the season, winning 10 of their 12 league games. They lead Brazil’s top flight, seven points clear of nearest rival Gremio.
Castro leaves Botafogo to coach Ronaldo at Al Nassr – sources