A little over two years before the kickoff of World Cup 2014 in Brazil, nearly 40% of projects are yet to start, the government has said.
Brazil plans to spend $13bn on 101 projects to build or modernise stadiums, airports, roads and public transport ahead of the World Cup.
Work has only begun on 60 projects, the government has said, insisting there is no cause for alarm.
Football's governing body FIFA has for months complained about delays, but Brazilian Sports Minister Aldo Rebelo insisted preparations for the first World Cup in Brazil since 1950 remain on track.
"We are not working on the possibility or the assumption of a delay. We have an eye on the current state of the projects and another on their completion," said Mr Rebelo, flanked by Planning Minister Miriam Belchior and Cities Minister Aguinaldo Ribero.
Six of the 12 stadiums that are to host World Cup matches will be ready in time for the 2013 Confederations Cup, the government said.
"The projects are on schedule," said Mr Rebelo. "We expect the Confederations Cup will take place in the six planned arenas."
The Confederations Cup, seen as a dress rehearsal for the World Cup, will be held from 15 to 30 June next year in four confirmed cities: Rio de Janeiro, Brasilia, Belo Horizonte and Fortaleza.
Recife and Salvador could be added at a later stage depending on how work progresses.
The expansion and renovation of stadiums in the southern cities of Curitiba and Porto Alegre is less advanced than in other host cities.
Of particular concern is the mass transit system, particularly access to the host arenas for the millions of tourists who plan to attend the event, as well as the 2016 Summer Olympics.
As of April, only 28 of the 51 planned transport projects had begun. Bidding for seven others is under way and concessions for nine are in the process of being awarded.
Work has begun on only 13 of the 31 planned projects to upgrade airports.
"The government is optimistic and confident about overcoming all the challenges," Mr Rebelo said.
