Portanova had his original six-month suspension cut to four by the Italian sporting tribunal on Friday, infuriating the player and his lawyer Gabriele Bordoni who said the centre back was thinking about leaving the country.
"Why is it that for others the ban was reduced by 60 percent and for me by 40 percent?", asked the defender in an interview with the Corriere dello Sport newspaper on Saturday although the true percentage of his reduction was 33.
Juventus coach Antonio Conte's 10-month ban, for failing to report two incidents of match-fixing in the 2010-11 season when he was in charge of Siena, was cut to four earlier this month.
"I'm struggling to understand, I can't explain it, I didn't expect this," said the 33-year-old Portanova. "I have to be honest that I'm bitter.
"I'm innocent and I can look at myself in the mirror. I don't want to cause trouble but there are some concrete facts here.
"Why have they treated me differently?", added Portanova who can play again from December 8.