The former Parma keeper pulled out of the Azzurri's latest World Cup qualifier, citing a thigh problem, which led to claims that he did so in order to be in peak condition for the game against Napoli.
But Marotta has leapt to the defence of the 34-year-old and dismissed the theories as nonsense.
"There is nothing to say on Buffon," he stated to reporters.
"He is the captain of Juventus and the captain of Italy. The allegations made are unfounded.
"He didn’t play against Denmark because he thought he wasn’t ready. Ours is a nation of conspiracy. Everything needs to be taken back to sport.
"Wearing the blue shirt of Italy is the highest aspiration for all players and Buffon is not the kind of guy to quit at the first problem."
Another Bianconeri player who may miss Saturday night’s clash with Napoli is midfielder Claudio Marchisio, after the Italian international suffered a shoulder injury in the 3-1 win over Denmark on Tuesday night.