Maradona said he has not had drugs or alcohol for six years in Friday's edition of the Clarin newspaper. Grondona implied in a television interview this week that Maradona was using again.
"There are reasons for what happens (with Maradona) and everybody knows them," Grondona said.
Maradona said he has contacted his lawyers about filing the case, though it was not clear when that might happen.
He has been involved in a spat with the 79-year-old Grondona since July, when Maradona's contract as national coach was not renewed. Grondona offered to keep him on, but asked Maradona to fire some of his assistants. Maradona refused and was dismissed.
Grondona, who was also a FIFA vice president, hired Maradona in 2008.
Maradona has repeatedly accused Grondona of "betrayal" and has been just as angry with Carlos Bilardo, the general manager of the Argentina team and Maradona's coach on the World Cup-winning team in 1986.
In an interview on Monday, Maradona accused Grondona of being senile _ calling him "gaga" in Spanish _ and suggested he was receiving treatments several times a year at an expensive Swiss clinic.
Maradona has been unable to find work since being released by Grondona. Months after being let go he suggested he might replace his assistants. By that time it was too late, with Sergio Batista taking over the national team.
He has also lobbied to coach other clubs and this week criticized the choice of Julio Cesar Falcioni as the new coach of Boca Juniors, saying he should have been given the job at his old club.