Cartagena president Paco Gomez says his team were relegated from Spain's Segunda Division last season because six of his players were betting against their own team.
Cartagena spent were relegated to Spanish football's regionally-based third tier in June after finishing 20th of 22 teams with 40 points from 22 games.
Gomez told Spanish radio station Onda Regional on Tuesday evening that he had known well in advance that his side would go down, and that the authorities had looked the other way when he told them of his suspicions.
"I knew with ten games to go that Cartagena would go down, because some footballers were concentrating on betting," Gomez said. "I reported it to the Liga de Futbol Profesional. But here [in Spain] those who do these kind of things get away unnoticed."
Gomez claimed he had not gone public at the time as such goings-on were so widespread in Spanish football.
"If I had spoken about Cartagena last year they would have had to put half the footballers in Spain in prison," he said. "There are players earning between €40,000 and €50,000 per game and we had six of them last year, all starters. You cannot control that."
The recent widely-publicised revelation by Europol that at least 380 European games had been rigged in recent years did not include details of match-fixing in Spain. However, it has long been rumoured that such activity exists.
Spanish league vice-president Javier Tebas admitted last month that he knew La Liga games had been fixed in the past but said he did not have enough proof to act on his knowledge.
The Spanish footballing authorities had not followed the example of federations elsewhere in Europe that were acting to clean up the game, Gomez added.
"In Italy they throw them out, but here in Spain at the moment things have not been sorted out. There is as much shit here as in Italy, France, Germany and the others. I know who they are, but I cannot denounce them as I cannot show it."