Gillet, who has won nine caps for his country, was one of 20 people suspended over two matches involving his former club Bari in Serie B in 2008 and 2009.
The tribunal's appeal decision could now signal the end of the 34-year-old's career.
Bari finished in mid-table after losing 1-0 at home to Treviso in one of their final matches of the 2007-08 season and secured promotion a year later despite being beaten 3-2 at Salernitana.
The tribunal also rejected 11 other appeals including one from former Bari and Salernitana player Massimo Ganci, who was given a four-year ban, and ex-Bari player Gianluca Galasso who was suspended for three years and seven months.
In addition, it accepted a prosecution appeal against the acquittal of former Bari and Treviso player William Pianu and suspended him for three years and six months.
The tribunal also halved ex-Bari player Corrado Colombo's six-month ban on appeal while former Bari loanee Raffaele Bianco had his suspension of three and a half years reduced to six months.
Italy has been hit by a wave of match-fixing allegations in recent years with police investigating cases in Cremona, Bari and Naples.
Players affected by the decisions announced on Saturday can make one final appeal to the national sports tribunal TNAS.