Julio Grondona, Fifa's senior vice-president and one of the most powerful men in football, has died aged 82.
The Argentine, second only to president Sepp Blatter in the Fifa hierarchy, was taken to hospital in Buenos Aires on Wednesday with cardiac failure and later died, the governing body said.
Grondona had been head of the Argentine FA (AFA) since 1979 and a member of Fifa's executive committee since 1988.
Writing on Twitter, Blatter said he was "sad for the loss of a great friend".
The South American Football Confederation (Conmebol) confirmed Grondona's death in a statement, adding that he would be remembered for "giving his country recognition in football".
The AFA responded to the news by announcing the postponement of all matches in Argentina's domestic leagues this weekend as a mark of respect.
The governing body also announced a halt to all administrative functions until Monday, meaning a press conference at which Argentina coach Alejandro Sabella was due to confirm his future has been postponed.
During Grondona's time as head of the AFA, Argentina won the World Cup in 1986 and lost the final in both 1990 and 2014.
He had been due to step down from his AFA role when his current term came to an end in 2015.
Argentina forward Lionel Messi was among those to send condolences after the announcement.
"It's a very sad day for football, for all of Argentina and for me," the Barcelona forward wrote on his Facebook account.
"Our president, Julio Grondona, you have left us. I want to send my sincere condolences and a large hug to all his family members and friends."
Grondona made headlines earlier this summer after his troubled relationship with retired Argentina captain and manager Diego Maradona spilled into the public domain.
It was Grondona who hired Maradona as the national team coach, only to hastily dismiss him after Argentina lost in the quarter-finals of the 2010 World Cup.
During the tournament in Brazil last month, Maradona responded to being called a "bad luck charm" by Grondona by making an obscene gesture on live TV.