Giovani Moreno and Federico Santander had just pulled out of Racing Club's training ground in their car when another vehicle pulled in front of them and forced them to stop, Santander said.
Two men got out and threatened Moreno with a gun.
"They told Gio they would shoot him in the legs and would ruin his career," Paraguayan Santander told a radio interview late on Tuesday.
"I thought they were going to shoot him. He was terrified as I was. I'm frightened, I don't know what to do.
"They said that if we did not win the game, we would suffer the consequences."
Moreno's agent Agustin Jimenez told the Fox Sports cable channel: "They put a gun against his knee."
Argentine clubs are followed by groups of hardcore fans known as barras bravas, who are blamed for the country's chronic hooliganism problem.
