Miiko Albornoz, who plays for Helsingborg's bitter local rivals Malmo FF in Sweden's Allsvenskan, was in the stands to watch his brother Mauricio score twice for Brommapojkarna in a 4-2 loss to Helsingborg.
Convicted of the statutory rape of a 14-year-old girl in February, Miiko Albornoz was subjected to abuse from Helsingborg fans when they noticed him in the stands.
A section of the crowd began chanting that they were going to kill Albornoz after the game, which led police to escort him from the ground when the match was over.
"I condemn all threats, it doesn't matter who it is," Helsingborg director Paul Myllenberg told newspaper Sportbladet.
"We can't cut their tongues out unfortunately. We stopped doing that a long time ago in many parts of the world.
"There were some police officers there that escorted us, we had good help from them," said Malmo team-mate Jiloan Hamad, who was with Miiko Albornoz at the game.
Helsingborg top the Allsvenskan table on 44 points. Malmö are in second place on goal difference with a game in hand.