Cabanas, a key forward for Mexican club America as well as his country, could take years to recover from being shot in the head in a Mexico City bar on January 25.
Martino said Cardozo was having a fine season in Europe, a fact not fully appreciated back home where fans criticised his intermittent form for Paraguay.
Argentine Martino said Paraguayans overjoyed at seeing their idol Cabanas survive the shooting must get used to the fact he will not be at the World Cup and Paraguay need a good stand-in.
"There's a very big difference between what those of us in Paraguay think and what's really happening with 'Tacuara' (Cardozo) who, today, is one of the big names in world football," Martino said.
"And he has absolutely no doubts about the importance he has for us," he told local radio station 970.
Martino said Cabanas "has been producing one miracle after another" during his recovery and he and his staff had been giving the stricken player all their support but the coach had to think about how best to replace him for Paraguay.
The South Americans, who face holders Italy, Slovakia and New Zealand in Group F, must now look mainly to strikers Roque Santa Cruz, Nelson Haedo and Cardozo for their goals at the finals in South Africa starting on June 11.
"(Cardozo) has an objective that he's focusing on. He can play better or worse but he doesn't have mental ups and downs. He has the hardness (needed) for the big battles," Martino said.
