NRL chief executive Todd Greenberg says the game's crowd numbers in Sydney are aligned to the quality of stadia and is adamant the only way they can go through the roof is with the transformation of ANZ Stadium into a world-class, purpose-built rectangular venue.

Greenberg was stunned last week after being told in a meeting with Premier Gladys Berejiklian that there was no guarantee of a knockdown and rebuild of ANZ as part of the government's $1.6 billion stadia strategy.

The NRL is opposed to a cheaper alternative, a modification of the Sydney Olympic Park venue, which would bring the lower bowl closer to the field but leave the upper tier as is.

Greenberg's desire is for a new 70,000-seat stadium on the ANZ site to accompany the 30,000-capacity venue being built at Parramatta and due to open in 2019, with Allianz Stadium to be refurbished as well if possible.