Reports also said another accused player, ex-Piacenza defender Carlo Gervasoni, had told prosecutors that many more Italian matches than previously suspected involved illegal betting and match-fixing including games in Serie A.
Promoted top-flight side Atalanta had six points deducted and Doni was banned for three-and-a-half-years in August after a football federation probe into betting in Serie B last term, but Doni had never previously admitted his guilt.
On Tuesday, the ANSA news agency published his testimony in front of criminal prosecutors where he said he engaged in illegal betting "only because of the passion which linked me to my team and the hope of being able to help them to the objective [of promotion] that season."
Atalanta, thriving in 11th in Serie A despite the deduction, issued a statement last week saying they had reacted with "surprise and great bitterness" after hearing rumours Doni had admitted involvement following his arrest this month.
Another 16 people were arrested as police, following up on the football federation investigation, said it had evidence of connections between the accused and criminal groups in Singapore and Eastern Europe.
Italy has only just got over a previous match-fixing scandal which led to Juventus being demoted from the top flight in 2006 and stripped of two league titles.
Juve have only now fully recovered from the blow and are joint-top of Serie A at the mid-season break.
