The Wall Street Journal uses data it says was released on Monday by Brazil's airport authority, the National Civil Aviation Agency, or ANAC.
The report claims São Paulo–Guarulhos Airport, the largest in Brazil by capacity, had 87.8% of World-Cup-related work done by January, when 92% was supposed to be finished.
Campinas–Viracopos Airport, also serving São Paulo, was 81.9% done, while it should have 85.36% and Brasilia's Juscelino Kubitschek Airport had 78.3% of the renovation work done, compared with 87.9% expected for January.
The report is focused on the three airports operated by private-sector firms, and will handle extra traffic due to the international tournament, taking place from June 12 to July 13.
The Brazilian airport authority gave assurances the projects will be completed in time for the start of the World Cup, when 12 Brazilian cities host matches, and 600,000 foreign visitors are expected to make the trip.
And it says it is increasing inspections and working with airport operators to make sure all the work is finished by May 11 in Viracopos and Guarulhos, and by May 24 in Brasilia.