The coach praised the Real Madrid man but suggested that Germany's opponents at the World Cup rely heavily on the forward
The Real Madrid attacker scored all four goals in the 4-2 aggregate play-off win over Sweden which sealed the Seleccao's spot in Brazil after they struggled in the initial Uefa qualification phase.
Low's side, who comfortably sailed into their 15th successive World Cup, praised Ronaldo but suggested Portugal do not have many other players to drag them out of a group including Germany, Ghana and USA.
"Cristiano Ronaldo justifiably won the Ballon d'Or for his performances last year, he seemed to score two or three goals in almost every game he played in, including for Portugal," the trainer told DPA.
"In the play-off with Sweden he decided everything yourself, pretty much. Although they have other good players, Portugal are very dependent on Cristiano Ronaldo."
Ronaldo will head into the tournament having endured a troubling couple of months. He missed the Copa del Rey final due to a muscular problem and remains a minor doubt for the Champions League showpiece later in May.
He is expected to be rested in Real Madrid's final game of the season on Saturdayat home to Espanyol, as Carlo Ancelotti looks to keep him fit to face Atletico Madrid as the team chase La Decima on May 24.
Low made some unexpected alterations to his squad on the back of a 0-0 friendly draw with Poland on Tuesday, most notably Borussia Monchengladbach midfielder Christph Kramer was brought in while forward Andre Hahn was dropped entirely.
Leon Goretzka and Max Meyer - both of Schalke - and Hamburg's Marcell Jansen have been demoted to back-up players for the World Cup squad should his core group of 27 players, still to be cut to 23 before June 2, pick up injuries.