Ronaldo ended in nine years spell at the Bernabeu this summer securing a move to Juventus for £105m.
The Portuguese had helped Real Madrid to a third consecutive Champions League trophy before securing his exit.
The 33-year-old scored 15 goals in the UCL last season as Real Madrid defeated Liverpool 3-1 in the final in Kiev.
And Argentine ace Messi admitted his shock over Ronaldo’s move when discussing his transfer publicly for the first time.
“Real Madrid are one of the best teams in the world and they have a great squad,” Messi said to Spanish radio station Catalunya Radio.
“[But] It’s evident that the absence of Ronaldo makes them less good and makes Juventus clear favourites to win the Champions League.
“It surprised me. I didn’t imagine him leaving Madrid or joining Juventus.
“There were a lot of teams that wanted him. It surprised me, but he has gone to a very good team.”
And Messi has also made it clear success in Europe in Barcelona’s goal for the season.
Messi added: “It’s time [Barcelona won the Champions League]. We have been knocked out in the quarter-finals in the last three seasons
“Last season’s result in Rome hurt especially, but we have a spectacular squad and we can fight for it.”
Barcelona have started the new season well and currently sit top of La Liga after thrashing Huesca 8-2 over the weekend.
Messi’s brace made him joint top-scorer with Real Madrid’s Karim Benzema on four goals.
After the two-weeks international break, Barcelona face Real Sociedad on Saturday 15th September.