Salvadorian businessman approached the players with financial inducements before they travelled to Canada for the match at the weekend.
El Salvador players were offered financial inducements to win, draw or avoid a heavy defeat in their crunch World Cup qualifier against Canada, the country's football association said on Tuesday.
"Players with the national football team reveal the supposed arrangement ahead of their game with Canada," the association said on the team's Facebook page.
A heavy defeat for the Salvadorans in Tuesday evening's match in Vancouver could prevent their neighbours Honduras from progressing to the final stage of CONCACAF qualifying for the 2018 World Cup finals in Russia.
Honduras are in pole position to advance but Canada could edge them on goal difference if they run up a big score against El Salvador and Honduras lose to Group One leaders Mexico at the Aztec stadium.
Mexico are unbeaten in five matches and the Salvadorans sit bottom of the group with two points from a possible 15.
The association said a Salvadoran businessman and former president of local club Alianza FC approached the players with financial inducements before they travelled to Canada at the weekend.
"Players with the national team tonight revealed at a press conference a tape in which the Salvadoran businessman Ricardo Padilla offered them 'rewards' for winning, drawing or even losing against Canada," the association said.
Team captain Nelson Bonilla played the tape of the 10-minute conversation to reporters in Vancouver on Monday night.
In it, the man identified as Padilla promised varying amounts of money depending on the result and the time played by each player, from $30 a minute for a win to $10 a minute in a 1-0 defeat.
"In reference to what we heard, we want to make it clear that we are against anything of this kind," Bonilla said.
"We want to be transparent about everything that has happened with the national team."
Fourteen El Salvador internationals were banned for life for match-fixing in 2013.
FIFA said it was aware of the issue and was looking into the matter.
"FIFA does comment on whether or not investigations are underway into alleged cases of match manipulation so as not to compromise any possible investigations," a spokesperson said.
CONCACAF did not respond to emailed requests for comment and the football associations of Canada, Honduras and Mexico made no mention of the allegations on their websites.
Padilla, however, said there was nothing wrong with the offer as he was not asking the players to throw the game.
"Let them investigate, I'm not worried," he told the Salvadoran newspaper La Prensa Grafica. "Those who want to see it as something bad can see it that way and those who want to see it as something good then they can too."
Relations between El Salvador and Honduras have not always been harmonious on the soccer pitch and the two Central American nations went to war in 1969 after a rancorous best-of-three World Cup series.
The short-lived conflict had been brewing for months but angry scenes during the matches led to border skirmishes in which hundreds of people were killed in what was forever remembered as the Soccer War.