Jordan Larsson, a 19-year-old striker, looked to have fired his side to safety when he scored against Halmstad in the 83rd minute of Sunday's relegation-promotion playoff clash at the Olympia.
However, a Marcus Mathisen double in the last three minutes gave the second-tier side a 3-2 aggregate victory and saw Helsingborg drop out of the Allsvenskan.
In the aftermath of the match, a number of masked men entered the field and tried to take off Jordan's shirt before one fan appeared to strike the teenager.
This prompted an angry response from Henrik, who stood up to the men before security came to Jordan's aid and defused the situation.
Speaking after the game, the Celtic and Barcelona legend is quoted by The Sun as saying: "I didn't see that they attacked Jordan, but if I had I would have gone in there and started hitting.
"I will look over my shoulder a but more and not walk alone in the city. If they want to come, come, we have got lots of dogs at home."
The seven-time Swedish champions were relegated for the first time in 23 years, with Larsson having been in charge of the club he used to play for since the start of last season