Mauri, 34, was banned for six months in early August before the Italian Football Federation added three months to his suspension after an appeal in October.
The veteran was found guilty of failing to report match-fixing in the Lecce versus Lazio Serie A match in May 2011.
But the reduction after an appeal to Italy's National Tribunal of Sporting Arbitration (TNAS) could see Mauri return on February 2 and potentially line-up for his side in the derby against Roma a week later.
"The TNAS, in relation to arbitration Stefano Mauri and FIGC announced that the Arbitration Board ... partially upheld the demand for arbitration and, accordingly, upheld the decision of the National Disciplinary Committee dated 2 August 2013, in which the player was imposed the penalty of six months suspension," a statement from the TNAS said.
Mauri tweeted: "It is almost over."
More than 50 people have been arrested in Italy for match-fixing since mid-2011.
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