"The cheque has cleared and therefore puts in motion the process of the transfer," said a Barcelona club source.
The French Football Federation (FFF) and French league (LFP) confirmed to AFP on Friday that the player's transfer certificate had been received from the Spanish Football Federation (RFEF).
That will allow him to be registered for the game at the Stade du Roudourou.
"Neymar's contract will be ratified during the afternoon. He will be able to play on Sunday," said the LFP.
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However, he had to watch last weekend's 2-0 win over Amiens from the stands as the administrative formalities of the deal were not completed in time.
FFF president Noel Le Graet had earlier stated his confidence that Neymar would be able to make his bow in Brittany.
"There is no reason for this hold-up to continue," he told French sports daily L'Equipe.
"I do not doubt that this will be quickly solved.