The Australian investment bank is acting as a so-called IPO advisor and will help select several banks to lead the planned listing as global coordinators, they said, adding the mandates will likely be awarded later this month.

Novomatic, owned by the family of its billionaire founder Johann Graf, makes slot machines and other gambling equipment and technology. It also operates casinos and a network of sport betting shops.

The listing would likely take place in the second half of the year in London, although Frankfurt remains an option, one of the sources said. Macquarie and Novomatic declined to comment.

The company is looking to list roughly 20-30 percent of its stock, one source said. At a valuation of more than 6 billion euros, that would make it one of the biggest ever IPOs of an Austrian company.

Telekom Austria's (>> Telekom Austria AG) raised 1.2 billion euros in an IPO in 2000, Raiffeisen Bank International (>> Raiffeisen Bank International AG) raised 1.1 billion euros in 2005 and construction firm Strabag (>> Strabag SE) raised 1.3 billion euros in 2007, shortly before the global financial crisis hit and put the brakes on company listings.

Novomatic employs roughly 28,000 people and has subsidiaries in 50 countries, according to its website. It generated revenue of 3.9 billion euros in 2015.

($1 = 0.9469 euros)

(Reporting by Arno Schuetze; additional reporting by Shadia Nasralla and Francois Murphy in Vienna; Editing by Harro ten Wolde/Keith Weir)