Napoli have been docked two points and fined 70,000 euros ($92,000, 57,000 pounds) in connection with a long-running probe into illegal betting, the Italian football federation (FIGC) said on Tuesday.
The southern Italy club's captain Paolo Cannavaro and fellow defender Gianluca Grava were banned for six months for "failing to report evidence of corruption", the federation added.
Napoli, who have said they would appeal the sanction, were in third spot before the ruling but now fall to fifth, 10 points behind defending champions and league leaders Juventus, in a severe blow to their title hopes.
The FIGC disciplinary committee also said it had suspended former goalkeeper Matteo Gianello for three years and three months for his involvement in an attempt to fix the match between Napoli and Sampdoria on May 16, 2010.
The sport authority hearing is separate from a wider criminal investigation into suspect matches headed by prosecutors in three Italian cities that has implicated players from the top flight and second-tier Serie B.
This season, Serie A sides Sienna have been docked six points, Atalanta two and Torino one as a result of the illegal betting investigation.