Tax officials in Brazil have been examining the 23-year-old’s accounts for more than a year, according to reports.
Federal prosecutors said they hope to file charges against Neymar – who’s set to face Juventus in tonight’s Champions League final – in the next few weeks.
They are apparently investigating an “unusual” cash flow of £24m at his parents’ company between 2011 and 2014.
Neymar moved to Spain in 2013 from Santos, but the Brazil club took legal action over the controversial move.
The star defended the deal – and the profit his father made from it – last year.
He said: “I’ve been quiet until now, but I can’t go on listening to all these things about my transfer.
“A lot of people come out and talk a load of rubbish – calling our character into doubt.”
The striker has scored nine goals in this season’s Champions League, including a brace against Bayern Munich to reach the final.