Pantani, winner of the Tour de France and Giro d'Italia in 1998, was quoted as saying his American rival is "clever and he's making the most of his sickness".
He went on to say that that Armstrong is "nothing special" and is "not a great champion".
"I don't want to get into an argument, but for me Armstrong is nothing special," Pantani told the Spanish sports daily Marca.
Pantani, who has been the target of doping investigations in recent years, did offer that Armstrong is "a great rider".
Armstrong, 30, overcame testicular cancer to win the Tour de France the last three years.
Pantani and Armstrong have regularly exchanged insults in recent times.
On more than one occasion, Armstrong has referred to the Italian as "Elefantino" in reference to his large ears.
And Pantani was angry when Armstrong eased up to let him win a stage of the Tour two years ago.