In what is becoming a regular pattern, Fifa has been forced to insist hurriedly that Sepp Blatter will not stand again for the presidency and will “lay down his mandate” as promised.

Blatter sparked a fresh wave of speculation when a Swiss newspaper reported him as saying: “I have not resigned, I put my mandate in the hands of an extraordinary congress.”

With a typically obtuse flourish, the 79-year-old added: “Only those who know the past can understand the present and shape the future. Or in other words: the ball is round – but only those who come from outer space know the actual dimensions of our sport … For me personally, the museum is a labour of love. But do not get me wrong: I’m not ready for the museum nor for a waxwork yet.”

Fifa said that his comments, at an event held at the Fifa museum in Zurich, were in line with his speech on 2 June when he did not mention resigning but did promise to lay down his mandate at an extraordinary congress between December and March.

In that same speech he said: “I shall not be a candidate,” and said the election, most likely in December, would be for his successor. Fifa insiders were quick to insist that he would not be standing again, despite the inevitable speculation that he might perform a U-turn given his history.

He said in 2011 that his fourth term as president would be his last, only to stand again in 2015 and win, before promising to step down four days later given the maelstrom engulfing Fifa as a result of twin US and Swiss criminal investigations.

The comments, and recent on-the -record quotes by his former adviser Klaus Stöhlker, are being viewed by many as an attempt to destabilise his opponents, including the Uefa president, Michel Platini.

Stöhlker, an adviser to Blatter during his re-election campaign, told the Guardian that Blatter would reconsider “if there was no other viable candidate” and that if he stood he would win.

The Fifa executive committee will meet on 20 July to decide a date for the extraordinary congress in what is expected to be the latest staging post in the politicking that has followed the dramatic events of late May, when 14 officials were charged in the US with a “World Cup of fraud” on counts of money-laundering, racketeering and fraud.

Fifa has yet to confirm whether Blatter and his secretary general, Jérôme Valcke, under pressure over what he knew about a $10m payment from South Africa to the Caribbean via Fifa that US investigators alleged was a bribe, would travel to Canada for the Women’s World Cup final, which takes place a week on Sunday. It had previously been forced to deny claims that Blatter was avoiding the US due to the continuing FBI investigation. “The travel plans of both the Fifa president and secretary general will be communicated in due course,” said a Fifa spokesman.