The Confederations Cup is a dress-rehearsal for the 2014 World Cup.
"Without the grass it would be like opening a theatre with no stage," Brasilia's World Cup secretary Claudio Monteiro said.
President Dilma Rousseff was scheduled to open the new 72,000-seater Mane Garrincha National Stadium on Sunday but contractors have not been able to drain the waterlogged ground enough to lay the turf.
Only four of the six Confederations venues are ready for the tournament.
The Mane Garrincha, where Brazil face Japan in the June 15 opener, is behind schedule along with the iconic Maracana stadium in Rio de Janeiro where the Confederations Cup final will be played.
Brasilia is now set to open its venue when the finalists of the city's local championship meet.
The teams will play before a crowd of around 30,000, representing the first of two test events required by FIFA.
The second test is expected to take place in front of a full house of 72,000 on May 26 when Neymar's Santos face Flamengo in the first fixture of the Brazilian championship.
The $500 million arena is the most expensive of the 12 venues that will host the World Cup.
The iconic Maracana is providing World Cup organisers with one of their biggest headaches.
The stadium is still receiving the finishing touches to a $400 million refurbishment, its third costly overhaul in 12 years.
The pitch has been laid and more than half the 78,000 seats have been installed but work is still being done on the roof while access areas have not been started.
The Maracana was supposed to be ready in December and that date has been repeatedly pushed back.
The earliest it will be handed over to FIFA is April 27 and may not be finished even then.
The Maracana's big test will come on June 2 when it hosts a friendly between Brazil and England.