One, players’ agent Christophe Henrotay, was held in Monaco. The other is said to be an associate in Belgium.
They were detained during raids on Tuesday and Wednesday.
Prosecutors said the arrests stem from an ongoing inquiry into the £13m (€18m) transfer of striker Aleksandar Mitrovic from Anderlecht to Newcastle in 2015.
“The facts involve notably money-laundering operations and private corruption in the context of football player transfers,” they said on Wednesday.
A search was also carried out in London, where a Metropolitan Police spokesman said they were assisting the Belgian investigation.
It is understood that Newcastle believe they are not directly connected to the inquiry.
In April, Anderlecht premises were searched. No-one was detained at the time.
A separate inquiry into suspected fraud involving transfers during the 2017-2018 season led to raids on premises linked to Anderlecht, Club Bruges and Standard Liège last October.