The La Liga stars are widely regarded as the two finest players of their generation, having picked up the last six Ballon d'Or awards between them and broken numerous scoring records.
Laudrup, who shone for Real Madrid and Barcelona between 1989 and 1996, told EFE: "I think they need each other.
"If one scores a hat-trick, the other tries to beat that. They are two of the best, not just of this era - in 30 years we'll be talking about them and the debate will be whether Messi, Cristiano, Maradona or Pele is the greatest of all time."
When asked who he would rather have in his team, the former Swansea City boss said: "Both would have to be in it, as they've clearly been the best two over the past four or five years."
Ronaldo's Real and Messi's Barca will contest the first Clasico of the season on October 25 at the Santiago Bernabeu.
Laudrup, the current manager of Qatar Stars League side Lekhwiya, represented his country 104 times, and also turned out for Lazio, Juventus and Ajax Amsterdam in a decorated playing career.