The plan was originally put forward in December by the by the Royal Bank of Scotland, Fortis and Banco Santander after the consortium took over the Dutch bank.
A spokeswoman for Belgium-based Fortis said: "Fortis has received verbal approval from the bank."
Yesterday Reuters reported that ABN AMRO's asset management arm will become part of Fortis in three weeks.
Fortis told the news agency that the combined asset manager will have 240 billion euros ($370 billion) under management and an equal split between retail and institutional clients.
Fortis Investments' chief executive Richard Wohanka said the group will cut 500 out of 2,600 jobs in the second quarter.
"It helps a lot that the companies were run fairly autonomously from the parent companies," Mr Wohanka said.
Fortis expects written approval of the merger transition plan by Thursday of this week.