Sarkozy, head of the conservative UMP party, travelled to Abu Dhabi for a "conference that was very private and very well paid," alleged the Marianne weekly, without specifying the amount.
Contacted by AFP, Sarkozy's office neither confirmed nor denied the report.
Sarkozy has come under fire as the conference allegedly took place on Monday, the day after a disappointing UMP loss in a by-election in eastern France where his party was beaten into third place behind the Socialists and the far-right Front National (FN).
Moreover, on Tuesday, the party gathered to debate the controversial issue of whether or not to urge its supporters to back their Socialist rivals in Sunday's second round to keep out the FN.
One UMP deputy, who declined to be named, said Sarkozy's alleged attendance was "regrettable".
"His head is elsewhere," said the official.
Another MP from Sarkozy's party, Thierry Mariani, criticised his slowness to respond.
"One can do conferences abroad. That doesn't shock me. But I think that on this affair (of the by-election), if we had reacted immediately, it would have spared us two days of psychodrama," said Mariani.