Premier-designate Philippe Couillard questioned the accuracy of the Radio-Canada news reports, saying there is "no evidence" the information is accurate.
He said he did not know the name of the member in question when pressed by reporters.
According to a report by the French-language network of the CBC, one re-elected Liberal and three former members of the legislature from the government of Jean Charest are being investigated following allegations of illegal fundraising.
Couillard, who said all political parties had been gripped by the ethics issue, later promised to lead a government that is "competent, responsible, honest and transparent."
In his speech, Couillard promised to be truthful with voters as well as vowing to protect Quebec's language and culture.
He also raised Quebec's attachment to Canada and promised the province would play a full part in the Canadian federation.
Earlier in the day, the Parti Quebecois urged the Liberals to shed light on the alleged infractions.
On Wednesday, former Liberal deputy premier Nathalie Normandeau rejected allegations she helped an engineering firm obtain a lucrative contract to build a water treatment plant in exchange for fundraising donations.
Normandeau, who served in the post under Charest, said she is willing to meet with investigators from the Charbonneau Commission corruption inquiry and Quebec's anti-corruption police squad.
Court documents released Wednesday say police searched the provincial Liberals' headquarters in Montreal last summer as part of an investigation into the awarding of an $11-million Municipal Affairs Department contract for a water treatment plant in Boisbriand, Que.
Anti-corruption officials allege in the documents that Normandeau intervened in favour of the Roche engineering firm against the advice of civil servants.
The documents also contain allegations that Roche helped to raise funds for Normandeau and the Liberals.
Normandeau insists she was never manipulated by anyone and was not involved in fundraising.
No charges have been laid so far as a result of the allegations.
The Liberals regained power last week with a majority government after being thrown out in September 2012 in large part because of voter anger over ethical issues.
Normandeau did not run in the April 7 election.