Fifa has moved to head off speculation that Sepp Blatter could stay on as president by pointedly making it clear that the adviser responsible for suggesting he might perform a U-turn no longer has a mandate to speak for him.

In the wake of speculation sparked by unattributed comments to a Swiss newspaper, believed to come from the 74-year-old Zurich-based communications consultant Klaus Stöhlker, Fifa said that Blatter stood by the statement he made on the day he promised to quit.

“Klaus Stöhlker’s mandate from the Fifa President ended on 31 May 2015. The Fifa president would like to point to his remarks from 2 June,” it said. In that statement, Blatter said he would continue until an extraordinary elective congress to be held between December and February next year.

A Fifa executive committee meeting on 20 July will set the exact date. But Blatter was clear in his intention to “lay down my mandate” and stated: “I shall not be a candidate.”

Scepticism from those insistent on fundamental reform is inevitable since Blatter also promised in 2011 that his fourth term as president would be his last before performing a U-turn and declaring his “mission” unfinished.

Stöhlker acted as an advisor to Blatter throughout his low key re-election campaign, when he was not supposed to draw on central Fifa resources, but his contract expired on 31 May.

Quoted elsewhere in the Swiss newspaper Schweiz am Sonntag, Stöhlker said Blatter had a “fair chance” of remaining in power depending on what happened in the coming months.

“It’s hard to find someone who is an equal. Blatter has built the organisation into a global, highly successful company – and he’s a top diplomat,” he said.

The flurry of speculation prompted the head of Fifa’s audit and compliance unit, Domenico Scala, to underline the need for a new president and for widespread reform.

Scala, who appeared alongside Blatter when he announced his departure, is understood to be adamant that the president must keep his promise to go.

“For me, the reforms are the central topic. That is why I think it is clearly indispensable to follow through with the initiated process of president’s change as it has been announced,” Scala said on Sunday.

The intervention from Stöhlker provides an insight into both the febrile atmosphere that has gripped Fifa since the dawn raids on the Baur au Lac hotel two days before Blatter’s re-election and the scramble among his coterie of official and unofficial advisers for his ear.

Stöhlker is believed to have thought that Blatter could hang on to power, while others told him that his situation was untenable following his re-election. Four days later, Blatter promised to stand down.

Meanwhile, the Confederation of African Football said it had not heard of any of its members asking Blatter to stay on.

“At CAF level we are not aware of any African countries who have written to ask Blatter to stay on,” Kalusha Bwalya, a CAF executive committee member and president of the Football Association of Zambia, said.

“We feel it is better to get on with our own work in the meantime and see what everyone has to say in the next months. Everybody is waiting for clarity.”

Further revelations are expected as more US court documents are unsealed and the arrest and extradition process continues. Fourteen executives, including nine current or former Fifa officials, were charged by a US indictment alleging a “World Cup of fraud”. Four more, including the former Concacaf general secretary Chuck Blazer, pleaded guilty.

However, even if Blatter were to stand down immediately, under Fifa rules his place as president would be taken by the CAF president Issa Hayatou, who has been closely associated with his regime for more than two decades, as the most senior Fifa vice-president until an election could be held.

In addition Fifa’s director of communications, Walter de Gregorio, left the organisation days after he told a joke about Fifa’s travails on television, but the Swiss report claimed he had clashed with Blatter because he was adamant he should quit as president.