OTPP has given up its preemption rights over the asset and agreed to information being circulated to potential buyers of Macquarie's stake, one of the sources said, without specifying what conditions the Australian investor met in return.

A spokesman for OTPP declined to comment.

OTPP bought 39 percent of Brussels Airport in 2011 and rights of first refusal on Macquarie's stake. It wanted Macquarie to provide limited information to prospective bidders as this may give a competitive advantage to those taking part in the initial stages of the process.

JP Morgan is still mandated to sell the airport, which had nearly 2.25 million passengers in April, a rise of 5 percent compared with the same month in 2017.

The Wall Street bank declined to comment.

Brussels Airport serves as a hub for Brussels Airlines, which was taken over by Lufthansa in 2016.

Macquarie wants to cash out as the fund in which it holds part of its stake has matured. Brussels airport is the last remaining asset of the Macquarie European Infrastructure Fund (MEIF) I, while the remainder of the stake is held in its MEIF III, which was closed to new investors in 2010.

According to ratings agency Fitch which upgraded the airport in May, earnings before interest, tax, depreciation and amortization (EBITDA) post-specifics increased to 308 million euros during the 2017 financial year.

Fitch said the airport had recovered since a 2016 bomb attack.

(Editing by Adrian Croft)

By Dasha Afanasieva and Clara Denina