The teenager claimed that Lewandowski, who has agreed to join Bayern Munich in the summer, struck him on the head in response to a rude gesture.
Bild claims Lewandowski has been reported to police by the youngster, who also gave the newspaper his account of the incident.
But 25-year-old Polish striker Lewandowski has denied he was overly aggressive.
In a note on his Facebook page, Lewandowski wrote: "I have been forced to react to what happened outside my house before the media make a big deal out of it.
"It's not up to me to teach 17-year-olds, who only act tough when they are in groups, how to behave, but I won't allow my family to be insulted.
"At the same time I want to make it clear that I did not resort to violence against the people who offended my private sphere.
"I hope this remains an isolated incident and that I can focus fully on playing the second half of the season for Borussia in peace and quiet."
Dortmund general manager Hans-Joachim Watzke has pledged the club's support, saying: "Robert swears he did not touch the boy in the face or hit him and I believe Robert 100 per cent."
Lewandowski plays his first game for Dortmund since his move to Bayern was confirmed when he faces Augsburg on Saturday.