In a surprise development, multilingual lawyer Infantino, who has been Uefa's General Secretary since 2009, entered the running to succeed Sepp Blatter with the "full backing" of the Union of European Football Associations' executive committee.
With Infantino's candidacy the total number of declared candidates for the top job at the Zurich-based world governing body for football stood at eight.
He was joined on Monday by Bahrain's powerful Asian football chief Shaikh Salman bin Ebrahim al Khalifa who pledged to get the scandal-tainted organization "back on the right track."
Infantino's announcement would appear to place Platini, the Uefa president who is currently serving a 90-day ban as investigations continue into a $2-million payment received from Fifa in 2011 without a written contract, in an uncomfortable position.
"We believe that Gianni Infantino has all of the qualities required to tackle the major challenges ahead and to lead the organization on a path of reform to restore Fifa's integrity and credibility," said Uefa, based in Nyon, Switzerland.
"We are delighted that Gianni has agreed to stand and he knows that he has our full support in his campaign to become Fifa president."
Erstwhile favourite Platini officially remains a contender pending an examination of his candidacy when his ban ends on January 5th.
But it remains to be seen whether he has now lost all support from his own organization or whether Infantino is being presented by Uefa as a Plan B in case the former France star is prevented from standing.
Another potential pitfall for Platini is that Fifa's electoral committee must judge the integrity of all candidates, and their evaluation could be influenced by his ban.
Platini's lawyers confirmed he had had a first appeal against his ban rejected on Monday, but the case is still to go before Fifa's appeals committee and his lawyers said they remained "convinced the appeals will eventually show his complete integrity and restore all his rights."
Asian football chief Shaikh Salman also left it late to officially announce that he had entered the race to succeed Blatter.
The 49-year-old Bahraini royal has been the head of the Asian Football Confederation since 2013 and is familiar with Fifa from his role as a vice-president.
He previously supported Platini's bid.
Salman said in a statement that he had decided to run "out of a wish to put the international organization back on the right track and in response to calls by many members of the football community."
However, even without Infantino's announcement, his chances of receiving the backing of European federations may not have been helped by the fact he has been heavily criticized by human rights campaigners for his role in
suppressing pro-democracy demonstrations in Bahrain in 2011.
Another heavyweight candidate to come forward is Tokyo Sexwale, the 62-year-old South African anti-apartheid campaigner who was once jailed alongside Nelson Mandela, serving 13 years of an 18-year sentence on Robben
Island on terrorism charges.
His non-footballing background could serve as an asset but also as a handicap, given that it is the presidents of Fifa's 209 member federations who elect the president.
Other confirmed candidates include the Jordanian Prince Ali Bin Al Hussein, the 39-year-old brother of Jordan's King Abdullah who was the only adversary to Blatter at the election in May this year and can boast that he took the veteran Swiss to a second round of voting before withdrawing.
But on that occasion he had the backing of Uefa, something he is likely to have to do without this time.
French former diplomat Jérôme Champagne, 57, spent 11 years working for Fifa between 1999 and 2010.
Unlike during his previous bid in May, he has managed to get the five signatures from national associations needed.
But he appears to lack the necessary clout, a problem also faced by David Nakhid, the former Trinidad and Tobago captain who once played for Swiss side Grasshoppers Zurich.
In addition, Liberian FA chief Musa Bility confirmed to AFP on Monday that he had entered the race, becoming the eighth runner to replace Blatter.
"I have officially presented my bid for the presidency of Fifa. I am very optimistic that I will win the presidency of Fifa and I promise to bring positive changes," Bility said.
Fifa's electoral committee is set to meet on Tuesday to study each bid and the integrity of the candidates, with the exception of Platini, who must wait until the end of his ban.
One name which will be missing will be that of South Korean businessman Chung Mong-Joon, who announced on Monday that he was withdrawing because of a six-year ban imposed on him by Fifa's ethics committee.