GENEVA -- FIFA's long-time legal director who was a key link to its American lawyers during federal investigations of corruption has left soccer's world body.

Marco Villiger, now the deputy secretary general for administrative matters, left the organization on Monday after more than a decade, FIFA said in a statement announcing the exit of its highest-ranking official to stay in office during recent years of turmoil.

Villiger said in FIFA's statement he was "seeking for new challenges" after a successful World Cup in Russia.

He was the main FIFA official to remain and have continuing influence during investigations by United States and Swiss federal prosecutors which were revealed in May 2015 and are ongoing.

Then-FIFA president Sepp Blatter announced his intention to resign within days, and has since been critical of the Swiss lawyer's role in the transition.

Villiger was responsible for hiring legal firm Quinn Emanuel Urquhart and Sullivan to protect FIFA's interests even before sweeping indictments were published. In 2014, the New York Daily News had reported former FIFA executive committee member Chuck Blazer was co-operating with American federal authorities.

Blatter told reporters in March this year he was "totally disappointed" with Villiger, whom he had regarded as a loyal confidant with detailed knowledge of FIFA's business.

"He knew it. All contracts went on his desk and he was the secretary of all the committees of FIFA," Blatter said of Villiger, who was promoted when Gianni Infantino was elected FIFA president in 2016. "He (Villiger) was the man who had all the power and Gianni was intelligent enough to keep him."

Under Villiger's legal guidance, FIFA portrayed itself to U.S. authorities as a victim of corruption instead of complicit, and has applied for tens of millions of dollars in restitution from assets forfeited by soccer and marketing officials who have pleaded guilty of bribery linked to broadcasting and commercial rights deals.

FIFA secretary general Fatma Samoura said Villiger "has been a pillar of the organization."

"I congratulate him wholeheartedly on his great career within FIFA, in which he has consistently demonstrated his expertise and professionalism, as well as his dedication to this great organization," Samoura said.