Players and coaches at Bulgarian first division club Lokomotiv Plovdiv have been told to take lie detector tests after their surprise 1-0 loss to basement side Botev Vratsa on Saturday stoked concerns about match-fixing.
Lokomotiv, Bulgarian champions in 2004, suffered their first loss of the season to lowly Botev Vratsa, who had been bottom of the table after a run of five consecutive defeats.
Lokomotiv's owner Veselin Mareshki told local media on Tuesday he had to be sure there were no other factors behind the team's loss.
"Nobody is insured against defeats but this loss is very strange," Mareshki said.
"The fair play principle is the most important thing for me and all players and coaches will take lie detector tests."
Earlier this month, the Bulgarian Football Union (BFU) said a prosecutor has opened an investigation into claims of match-fixing in four domestic games this season.
Spartak Pleven's junior team have been expelled from the domestic U-19's championship for match-fixing even before the results of the investigation have been announced.
Most games in the Balkan country's junior championship are included on bookmakers' betting coupons.
Media reports have claimed match-fixing and corruption have been rife in Bulgaria for years, but no one has been brought to trial with the European Commission criticising the authorities for doing little to fight the problem.