Schumacher suffered severe head injuries in a skiing accident at the end of 2013 and, after several months in hospital, returned to his Swiss home in September 2014.
Schumacher's manager, Sabine Kehm, has given no official update on the German's condition since December 2014, when she stated that he faced a "long, hard fight".
"I have news and unfortunately it is not good," di Montezemolo, who served as Ferrari President from 1991-2014, was quoted by news agency Reuters, refusing to elaborate.
In November, Jean Todt, President of Formula 1's governing body, the FIA, said that Schumacher was "still fighting" to overcome the injuries, almost two years on from the incident.
Kehm has refused to respond to di Montezemolo's comments.