Mr Cox yesterday confirmed he has applied to join Fine Gael through his local St Luke’s branch in Cork city ahead of an expected presidential bid.
The three-times MEP for Munster and former president of the European Parliament has also written to Fine Gael general secretary Tom Curran, requesting the approval of the party’s executive council for his membership application.
He is believed to have the backing of the party leadership but faces a tough battle to secure the party’s nomination from Ms McGuinness, who has vowed to appeal to the grassroots of the party to secure the nomination.
He will also be up against Dublin MEP Gay Mitchell, who is considering putting his name forward.
Mr Cox was in Fianna Fáil before representing the PDs in the European Parliament. But the 58-year-old has been closely associated with Fine Gael recently, helping in its strategy for the first 100 days in government, specifically in relation to the EU/IMF bailout.
The Fine Gael executive council will meet on June 14 when it will formally accept Mr Cox’s membership application and decide the time schedule for the selection process.
A spokesperson said the list of nominations will be available before the end of the month and a selection convention is likely to be held in early July.
Both Fianna Fáil and Sinn Féin have not yet decided whether to put forward a candidate or offer their support to an independent.
Both parties said they have not had any contact with the Irish-American lobbyist and journalist, Niall O’Dowd, who said he is confident of the support of at least 20 Oireachtas members required to run as an independent.