Video footage posted on social media showed 19-year-old Jordan Larsson being confronted by a group of hooded Helsingborg supporters at the end of the 2-1 defeat to Halmstad on Sunday and forcibly having his shirt removed.
The forward had scored to put his side ahead with eight minutes left against Halmstad, but two late goals from Marcus Mathisen condemned Helsingborg to relegation from the Allsvenskan after a 3-2 aggregate play-off defeat.
Fans were also seen trying to confront former Celtic, Barcelona and Manchester United striker Larsson, who has been in charge at his hometown club - with whom he had two spells as a player - since 2015.
A statement from director Mats-Ola Schulze on the club’s website read: “The events that took place after today’s game were unacceptable. Helsingborgs IF strongly reject this because it is contrary to our values . We will return with a statement about this when we have created a comprehensive picture.”
Manager Larsson earlier said he understood the fans’ anger but would be more aware of his safety in the town.
He told the Swedish press: “I understand their frustration. That’s why I went over there too. It was not the smartest thing for me to do.
“I did not see that they were attacking Jordan, but if I had I would have gone in there.
“I live and work here in town. I will look over my shoulder a little more and make sure not to walk alone in town.
“If they (hooligans) come, they come. We have many dogs at home.”