Switzerland's attorney general is leading 25 separate investigations into suspected corruption linked to Fifa and World Cup bidding.
The office of Michael Lauber confirmed the scale of "football-related cases" after securing a first conviction since its Fifa probes began in 2014.
Cases were not specified, but criminal proceedings are open against former Fifa officials Sepp Blatter and Jerome Valcke, and some 2006 World Cup organisers including Franz Beckenbauer.
Swiss and US prosecutors worked together on a guilty plea this week from Jorge Arzuaga, a former employee of Swiss private banks from Argentina.
Arzuaga admitted conspiring with former Fifa finance chairman Julio Grondona and others in a money-laundering conspiracy linked to bribes.
Mr Lauber's office said Arzuaga forfeited 650,000 US dollars (£510,000) in "unlawfully obtained" bonuses to the Swiss treasury.
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