The Portugal skipper joined Al-Nassr in January on a contract estimated by some media reports to be worth more than 200 million euros.
Ronaldo has played in three of the world's top leagues with stints at Real Madrid in Spain's La Liga, Manchester United in the English Premier League and Juventus in Italy's Serie A.
The forward said the quality of the Saudi competition had improved even in his short time in it.
"We are much better and the Saudi league is getting better and the next year will be even better," he told Saudi SSC channel on Tuesday.
"Step-by-step I think this league will be among the top five leagues in the world but they need time, players and infrastructure.
"But I believe that this country have amazing potential, they have amazing people and the league will be great in my opinion," he added.
The Saudis do not lack ambition and a source told Reuters earlier this month that Riyadh club Al-Hilal had made a formal offer to secure the services of Lionel Messi, Ronaldo's rival for the title of best player of his generation.
Ronaldo scored a stunning winner on Tuesday as Al-Nassr fought back to beat visitors Al-Shabab 3-2 and put Al-Ittihad's Saudi Pro League title celebrations on hold.
