Thousands of car spaces would be built above and below ground at Moore Park on land now used for playing fields, under secret plans for the precinct.

A mountain bike course would also be built, as well as function centres and indoor sports facilities, according to the plans developed but not released by the Centennial Park and Moore Park Trust.

The plans, aimed at setting the direction for the inner-east Sydney park for the next 25 years, propose to "increase car parking spaces" in the precinct.

They also propose converting the Hordern Pavilion and the Royal Hall of Industries into "high-performance indoor sports facilities".

The Member for Sydney, Alex Greenwich, said his main concern with the proposals was that they compromised and commercialised public land.

"When you look at car parks, it's a 'build it and they will come' model," said Mr Greenwich. "It will actually create more car traffic, adding to the congestion in the local area," he said.

The document shows the controversial $38 million "Tibby Cotter" bridge would link new underground and surface parking spaces on the western side of Moore Park to the Sydney Cricket Ground and Allianz Stadium.

These areas are not currently used for car parking. But the plans, first reported by the Wentworth Courier, reveal proposals for 3000 new car spaces.

Other development projects include a function centre on Mount Steel – the large grassy rise between Cleveland Street and Moore Park Golf Course.

And a mountain bike course could also be built at Mount Steel,

"This framework will set the 'future direction' for the park to 2040, establishing a blueprint to once again adapt to the pressures from an increased population and changing recreational trends," says the document, dated July 2, 2015.

According to the presentation, an extra 50,000 people will be living near the 150-year-old Moore Park in the next 20 years.

A spokesman for Environment Minister Mark Speakman, who has responsibility for the park, said: "This is a discussion document only."

"The trust is consulting with targeted stakeholders and once it has a clear picture of their feedback it will consult more widely with the community," the minister's spokesman said.

As well as the two-tiered parking at Moore Park west, there are also proposals for four-storey car parks with capacity for 3000 cars to the north of Moore Park and adjacent to Mount Steel.

Greens MP Mehreen Faruqi said the documents revealed the real thinking behind the Tibby Cotter bridge, which is rarely used other than when people are leaving the SCG.

"Did the public pay $38 million for a walkway between the SCG and an underground carpark – not for pedestrians and cyclists, but for motorists?," Dr Faruqi said.

The Moore Park proposals come as the Baird government considers whether to expand its original $600 million slated for stadium upgrades to include more lavish redevelopment at Allianz Stadium, ANZ Stadium and Pirtek Stadium, Parramatta.