The Real Madrid superstar had been given a short break following last weekend’s Champions League final victory over Liverpool.
Ronaldo arrived back in his homeland on Sunday and joined in training at Portugal’s Cruz Quebrada-Dafundo base in Lisbon.
He appeared in high spirits as the European champions stepped up their preparations for this summer’s tournament in Russia and stopped to sign autographs for fans after the session.
Portugal face Algeria in a warm-up clash on June 7 before opening their World Cup campaign against Spain later this month.
Fernando Santos had cut his provisional squad down to 23 players before Monday’s deadline.
Among those included are Manchester City playmaker Bernardo Silva, West Ham’s Joao Mario and Leicester new boy Ricardo Pereira.
William Carvalho, who is a target for new Everton boss Marco Silva, is also included.
Following last week’s win over Liverpool, Ronaldo fuelled speculation over his Real Madrid future.
The Los Blancos star insisted he would discuss his future after the win in Kiev – although he is yet to make any statement.
Zinedine Zidane’s depature, which was confirmed on Friday, is likely to have implications on Ronaldo’s decision.