Lazio have announced they are to bring legal action against Marcelo Bielsa after he informed them he would not be taking charge of the club this season, despite having already signed a contract.
The Biancocelesti said in a statement that Argentine coach Bielsa told them overnight that he has no intention of becoming their new head coach, despite their announcement just days ago that he had penned a deal with them.
The news comes two days after Gerardo "Tata" Martino quit as coach of the Argentina national team amid turmoil at the Argentine Football Association (AFA).
Bielsa, 60, was due to arrive in Rome on Saturday but will now not be flying to Italy. Simone Inzaghi, who coached Lazio in the second half of last season, has been placed in charge for the time being.
"We are shocked to learn of the resignation of Mr Marcelo Bielsa, also in the name of his assistants, which is in blatant violation of the commitment he assumed with the contracts signed last week and registered with the Lega Serie A and FIGC [Italian Football Federation]," read a statement from Lazio.
"The club reserves the right to take all the necessary action to protect its own rights. The team has been placed into the hands of Simone Inzaghi for the preseason training camp."
Lazio's solicitor Gian Michele Gentile has confirmed to Corriere dello Sport that he is getting straight to work on suing the former Argentina and Marseille coach.
"I've just heard of the news that Bielsa is not coming," he said. "Clearly this is a breach of contract on the part of the Rosario-born coach. Lazio will respond with legal action inevitably. [Club president Claudio] Lotito did everything to make him happy."
Bielsa's decision comes just days after the Lazio squad reported for preseason training, and hours before Inzaghi was due to accept an offer to take over at Serie B club Salernitana.
It is not clear whether Inzaghi will be appointed for the season or whether he will lead training until a permanent replacement can be found.
Former Italy coach Cesare Prandelli had held talks with Lotito before the Eternal City club turned to Bielsa and he may now be contacted once again.
Bielsa, who led Chile to the round-of-16 at the 2010 World Cup -- their first finals in 12 years -- returned to club management in 2011 with Athletic Bilbao. He led the Spanish clubs to the finals of both the Europa League and Copa del Rey in 2012, but was unable to build on that success the following year or emulate it in a subsequent spell at French club Marseille.
Last year, Marseille condemned Bielsa's sudden decision to resign as coach after the first match of the season. He was out of contract but had struck an agreement with club president Vincent Labrune to extend his tenure.
Bielsa said he changed his mind because Marseille officials allegedly amended the terms of the new deal at the last minute. Marseille's board of directors hit back, saying the club "can't submit itself to a single man's rule."
The previous season, Bielsa caused controversy early in his tenure when he publicly criticized Labrune for not consulting him during the transfer window, saying he did not get the right players.