Ronaldo, who was a free agent following his acrimonious split with Manchester United in November, joined Al Nassr last week on a 2-1/2 year deal estimated by media to be worth more than 200 million euros ($213.30 million).
"The signing of a player the size of Cristiano Ronaldo is extraordinary and contributes to the development of Saudi football," said Garcia, who previously managed Lille, AS Roma, Olympique Marseille and Olympique Lyonnais.
"We are happy with his arrival. The first goal is to work so he can adapt to our team, to enjoy playing for Al Nassr, and to entertain the fans."
Ronaldo will be unveiled at Al Nassr's home ground Mrsool Park, where 25,000 fans are expected to turn up.
The club, who lead the Saudi Professional League (SPL), have seen the number of followers on their Instagram account increase by millions since they announced Ronaldo's transfer.
The forward has scored 819 career goals and his arrival represents a coup for the Gulf country, which is looking to bring more big names to the SPL.
"We will support the rest of our clubs for qualitative deals with international stars soon," Abdulaziz bin Turki Al-Faisal, the country's Minister of Sports, has said.
"Cristiano, welcome to your new home, welcome to SPL."
