The probe follows a news report that Fifa sold the rights for rates below market value to a Caribbean football organisation.
Fifa said the agreement with the Caribbean group promised Fifa much more than the up-front fee.
Swiss Attorney General Michael Lauber told a press conference that prosecutors would look at the rightscontract “to see if it is really valuable [to the investigation] or not”.
He added that the probe as a whole was nowhere near the half-time whistle.
“Clearly we are not even near the half-time break,” he said.
The latest Swiss probe involves a 2005 contract to televise the 2010 and 2014 World Cups in parts of the Caribbean.
Swiss broadcaster SRF reported on Friday that Fifa signed over the media rights to the Caribbean Football Union (CFU) for $600,000.
It said that Jack Warner, head of the CFU at the time, then transferred the rights to his own company and resold them in a deal worth between $15m (£10m) and $20m.
SRF posted excerpts of the contract on its website that appeared to show that former Fifa boss Sepp Blatter and Mr Warner signed it themselves.
Fifa said in a statement that the CFU had promised it more than the upfront fee, and that Fifa was to receive half of any profits related to subcontracting the rights.
The organisation also said it terminated the contract in 2011 after the CFU failed to meet its financial obligations or follow subcontracting requirements.
Mr Lauber said his office had received an explanation from Fifa, which would be considered.
Mr Warner, who left organised football in 2011, has said in the past that he had evidence he was granted World Cup television rights in his region a number of times, including for the 2010 and 2014 events, in return for securing votes for Blatter’s campaigns for Fifa president.
He said the money made from media rights was used “to develop Caribbean football.”
Fifa has dismissed Mr Warner’s claims as false and said that television rights had nothing do with Mr Blatter’s election campaigns.
Mr Blatter has not been accused of misconduct by Swiss or US authorities.
In June a key figure in South Africa’s football World Cup bid broke ranks with the government to suggest there might be some truth to a claim that a $10m bribe was paid to secure the 2010 tournament.
Also in June, Swiss prosecutors said they were investigating 53 cases of possiblemoney laundering as part of an inquiry into bidding for the 2018 and 2022 Fifa World Cups.
Russia and Qatar, which are scheduled to hold the tournaments, have denied misconduct.