Soriano was speaking at a board meeting of European Football Clubs in Copenhagen before the organisation's general assembly on Tuesday.
According to the Press Association, Soriano told executives: "It's taken eight years to get here and it's going to take a lot more time", referring to the Premier League investigation that began in 2018.
He subsequently left the meeting without answering questions from the media.
Manchester City were accused of a wide range of financial rule breaches, including allegations that sponsorship revenue from connected companies had been inflated and that other payments were made off the books to circumvent financial regulations.
The club has been found guilty of the majority of the 115 charges brought by the Premier League, although sanctions have yet to be announced.
Premier League clubs are seeking legal advice about potential compensation relating to the charges, while City are expected to appeal against the ruling.
Possible sanctions include a points deduction, expulsion from the Premier League or a substantial fine, although no punishment has yet been confirmed.
Manchester United's chief of international football relations Jean-Claude Blanc was among those attending the Copenhagen meeting, alongside Everton owner Dan Friedkin, who was there in his capacity as owner of Roma.
City chairman Khaldoon Al Mubarak has also maintained that the club intends to prove its innocence. In a letter to supporters, he said the process remained ongoing and that City were confident in their position.
"The Premier League process still has a long way to run, and our confidence and intent in proving the club's innocence is just as strong as when this began," Al Mubarak said.
He added that there were many matters he would like to explain to supporters but that the confidentiality of the legal process prevented him from doing so.
City have also issued a statement saying the Premier League process remains ongoing, with significant elements still to be completed and subject to strict confidentiality.