Technical problems, shortages of funds and legal issues have recently marred Poland's preparations to co-host the European football tournament with Ukraine next year.
"Euro 2012 preparations have visibly advanced. But the scale of delays, abandoned projects and poorly implemented investments is so significant that it may threaten the smooth running of the tournament," Poland's Supreme Audit Office (NIK) said.
"NIK states that modernising the road infrastructure has suffered the most serious negligence," NIK, a state institution that is independent of the government, said in a report.
Prime Minister Donald Tusk, who made updating dilapidated infrastructure in the European Union's largest ex-communist member a priority ahead of Euro 2012, said Poland would be ready on time.
"Euro 2012 in Poland is not under threat. All the investments indispensible for the tournament to go ahead will be finalised," he told a news conference on Tuesday.
"I shall inform you shortly on how we plan to make up for the delays," he said, adding that not all the investments Poland had hoped to carry out for the June 8-July 1 tournament would come into effect.
On Wednesday in Warsaw, UEFA representatives are due to present their latest assessment of Poland's preparations.
Poland lags well behind most of its European peers in the size and quality of its road network, though Tusk's government has overseen a lot of projects since taking power in 2007.
"We are now seeing the Euro 2012 effect. Shortly after the games (have been played), we will probably already have to start repairing way too many of the new roads," Adrian Furgalski of the Transport Consultants' Group TOR told Reuters.
NIK said investment in the rail network and transport systems in Poland's four host cities - Warsaw, Gdansk, Poznan and Wroclaw - were also insufficient.
