The injured, identified as Sonu, who hails from Mundali, had a quarrel with the three fellow passengers over a window seat in the Delhi-Ambala train yesterday, they said.
In his statement, the youth said the three then assaulted and pushed him out of the running train.
He was admitted to a local hospital by police after a group of villagers sitting by the railway track informed them of the youth's condition.
A search is on to trace the accused, police added.