After several delays in the case, the latest due to France's coronavirus lockdown, the court heard arguments from parties on all sides behind closed doors on Wednesday.
Sources close to the case said the judges set a September 24 date to deliver their ruling.
Sarkozy has been charged over accusations by former members of Muammar Gaddafi's regime that he accepted millions from the slain Libyan dictator, some of it delivered in cash-stuffed suitcases, for his first presidential campaign in 2007.
He was charged in 2018 with taking bribes, concealing the embezzlement of Libyan public funds and illegal campaign financing.
The probe was sparked by investigative website Mediapart publishing a document in 2012 allegedly signed by Libya's intelligence chief and purporting to show that Kadhafi agreed to give Sarkozy up to 50 million euros ($62 million).
Sarkozy denies the charges. He maintains the document is a fake, but the courts have ruled it can be used as evidence.
Read also: French ex-leader Sarkozy decries 'mad allegations' amid Gaddafi corruption scandal
Sarkozy and his former ministers Claude Gueant, Eric Woerth and Brice Hortefeux challenge the validity of the investigation on a number of procedural grounds.
The former president is also seeking to invoke head-of-state immunity on some of the counts against him.
Several investigations into Sarkozy
The allegations that Sarkozy took money from Gaddafi - whom he welcomed to Paris shortly after his election with much pomp but later helped topple - are the most serious out of several investigations that have dogged him since he left office.
The claims first emerged in 2011, as NATO-backed forces were preparing to intervene in support of rebels seeking to end Gaddafi's tyrannical 41-year rule.
The investigation is also looking into claims by Franco-Lebanese businessman Ziad Takieddine, who said he delivered suitcases stuffed with a total of five million euros to Sarkozy and his then chief of staff Gueant in 2006 and 2007.
Sarkozy is already charged in two other cases, one relating to fake invoices devised to mask overspending on his failed 2012 re-election campaign, and another for alleged influence peddling - for which he will stand trial in October.
He has accused the French judiciary, with which he had a fraught relationship while in office, of hounding him.
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