The Manchester United legend played with Ronaldo for six years between 2003 and 2009, giving Giggs as good an opportunity as any to assess the undoubted talents of the Portuguese superstar.
But with the Ballon d'Or vote just around the corner, Giggs plumped for Ronaldo's big rival, Barcelona forward Leo Messi, when asked who he thinks is the current best player in the Europe.
In the Daily Star, Giggs was asked who is the greatest ever Champions League player, and he replied: "You have to think Messi. At the moment he is breaking all sorts of records.
"He is one of the greatest players to ever live and he has won it a couple of times.
"I would have to go for Messi. He is a goalscorer - he scores so many goals - but he is a team player as well.
"He sets up so many goals for his teammates and having experience playing against him, he is tough. It is difficult to get the ball off him.
"He can dribble, he can score any type of goal, left foot, right foot, headers. He has got so many assets - it's very, very tough to pin him down."
Giggs is set to come up against Ronaldo for the first time since the Portugal international made his £80m move to the Bernabeu in 2009, when Real Madrid take on Manchester United in the Champions League last-16 round.
Before that however, is the small matter of the FIFA Ballon d'Or. Ronaldo, Messi and Barcelona playmaker Andres Iniesta are the three candidates for this year's award, which will be presented on 7 January. Messi has received the last three trophies, while Ronaldo won it for the first time back in 2008 but is yet to win again since.