Barcelona overlooked serious hygiene issues at the club's 100,000-seat Camp Nou stadium, according to the company tasked with filing the report that uncovered the problems in 2013.
The report, put together by the company Gold Service, detailed how pigeon nests covered in excrement created bad smells and led to swarms of flies and mites gathering inside the ground.
There also was evidence of bird droppings falling into areas where food was prepared for supporters at Camp Nou, Barca's home since the 1960s.
"The situation was deplorable," Toni Mora, who signed off on the report, told RAC1 on Friday. "The word here is carelessness. The [pigeon] nests had probably been there for a couple of years, given the amount and size of them. If it was just a recent thing there would only have been a few twigs."
Mora explained that the accumulation of dirt in these areas, as well as in other parts of the stadium, led to huge hygiene risks for match-going fans.
The report called for an "urgent review" of the cleanliness of Camp Nou, but Barca never got back in contract with Gold Service to pursue the necessary action.
ESPN has contacted Barcelona for comment.
Earlier this week, La Vanguardia also revealed that Barca played 21 games at their home stadium in 2019 and 2020 despite serious structural problems.
The newspaper published reports that showed there was a "risk of fragments falling on supporters in walkways" and called for "immediate action."
Former president Josep Maria Bartomeu, according to the reports, was told of 127 problems that needed fixing urgently, 44 of which made the ground unsafe for fans.
New president Joan Laporta recently revealed that, when he was elected in March, Camp Nou was in a state of decay.
Laporta said the club have since taken action to get the ground back up to scratch, taking advantage of the fact last season's matches were played without fans due to the pandemic.
Despite that, Camp Nou is still in urgent need of an upgrade and, despite the club's financial problems, Laporta has revealed plans remain in place to give the stadium a facelift and expand the capacity to 110,000.
The work will be financed by Goldman Sachs, while Barca might have to spend a season away from Camp Nou while it is carried out, with the Estadi Johan Cruyff and the Olympic Stadium both options for temporary homes.