He left for Serie A club Napoli on 31 January 2008, joining fellow Brescia players Santacroce and Hamsik, for a total fee of €18 million within a season.

[3] In January 2009 he was handed a one-year suspension by the Court of Arbitration for Sport (CAS) along with former teammate Davide Possanzini from WADA for being late for a drugs test following a Serie B match between Brescia and Chievo in December 2007.

Mannini made an excellent start in his first season at Sampdoria, scoring 5 goals in Serie A and 3 assists in just 8 games.

Thus, both clubs had to submit a bid in a sealed envelope to Lega Serie A in order to decide the highest bidder, which was only €500.

[10] On 6 August 2011, Mannini moved to newly promoted Serie A club Siena in another co-ownership deal for €450,000 (plus €200,000 other fee) in a 4-year contract.

[18] Having been released by Pontedera, Mannini elected to retire from football, and moved to East Yorkshire to work as a sales executive for a food company.