Swiss Attorney General Lauber resigned last week over his handling of a corruption investigation targeting world football's troubled governing body.
A Swiss special prosecutor has launched criminal proceedings against FIFA president Gianni Infantino, authorities in Switzerland said, as part of an investigation into suspected collusion between him and the country's Attorney General, Michael Lauber.
In a statement, authorities said special prosecutor Stefan Keller "has reached the conclusion that...there are indications of criminal conduct" in relation to meetings between Infantino, Lauber and another official, Rinaldo Arnold.
"This concerns abuse of public office, breach of official secrecy, assisting offenders and incitement to these acts," the authorities said.
Infantino has not denied that the meetings took place and continued to defend his actions.
"To meet with the Attorney General of Switzerland is perfectly legitimate and it's perfectly legal," he said in a statement released by FIFA.
"It's no violation of anything. On the contrary, it is also part of the fiduciary duties of the president of FIFA."
Infantino and Lauber are said to have held a series of meetings in 2016 and 2017.
Two such meetings were initially exposed in 2018 by "Football Leaks", a cross-border investigation by several European news organisations.
Like Infantino, Lauber has denied any wrongdoing.
FIFA corruption scandal
Lauber was in charge of Switzerland's probe into the corruption scandal that exploded at the heart of FIFA in 2015.
The scandal erupted when Swiss police in May that year raided a luxury hotel in Zurich before dawn, arresting a number of top football officials.
The Swiss judiciary under Lauber quickly opened criminal proceedings against then-FIFA president Sepp Blatter and other top officials.
Blatter was eventually removed in 2015 and Infantino took over as FIFA president in 2016.
"It has been my aim from day one, and it remains my aim, to assist the authorities with investigating past wrongdoings at FIFA," Infantino insisted.
"FIFA officials have met with prosecutors in other jurisdictions across the world for exactly these purposes.
"People have been convicted and sentenced, thanks to FIFA's cooperation, and especially in the United States of America, where our cooperation has resulted in over 40 criminal convictions.
"Therefore, I remain fully supportive of the judicial process, and FIFA remains willing to fully cooperate with the Swiss authorities for these purposes."
Lauber, 54, has denied accusations that he lied about the meetings but is also under criminal investigation.
Relations with top officials
A Swiss parliamentary commission decided in May to open proceedings against Lauber over "well-founded suspicion of serious violation of the duties of office either intentionally or by gross negligence", which risked seeing him sacked.
Previously Lauber had been docked five percent of his salary, reduced from eight percent on appeal, following a disciplinary probe which found that he had repeatedly lied when questions were raised about the FIFA investigation.
Arnold, meanwhile, is a childhood friend of Infantino's who went on to become a senior prosecutor in Switzerland's Haut-Valais region where they grew up.
In April a Swiss newspaper, the Tribune de Geneve, alleged that Infantino wrote to Arnold after becoming "worried" about an investigation into him by the country's Office of the Attorney General (OAG) in relation to his awarding of a television rights contract to an offshore company in his previous role as UEFA's legal affairs director.
FIFA responded to that report by saying that emails referred to in the newspaper's article were "obviously obtained by hacking, which is an illegal and criminal act."