He described the perpetrators as having long beards but no moustaches, a style often preferred by Salafists. There were, however, no witnesses to the attack and police are currently searching for suspects.
It is not the first time this year that Bonn has hit the headlines as a result of possible Islamist activity.
In May, a Salafist was arrested after stabbing two police officers during a counter-demonstration against a display of caricatures on Prophet Mohammed by a local right-wing party.
Earlier this month, another member of the orthodox Muslim group threatened to take a hostage in order to force the perpetrator's release from prison.
Also in Dember, a bag full of explosives was found on a platform in Bonn's main train station in an apparent attempted bomb attack. While no charges have been filed in that case, clues reportedly lead to the Salafist community.
Meanwhile, police in Bonn are continuing their search for the two men who had demanded the student to convert to Islam and threatened to cut off his tongue if he refused.
So far, the police have no concrete information on the motive of the attack, but they have a strong suspicion that Islamic radicals may have been involved in the incident.
Therefore, a special police unit has taken up the investigations and it is cooperating closely with the state prosecutor in Bonn, the spokesman said.
The victim told the police that he was walking to a pub shortly after 10 on Christmas eve when two strangers approached him, picked up conversation and demanded him to convert to Islam.
They threatened to cut off his tongue if he refuses, the police commissioner in Bonn said in a press statement earlier.
As he tried to get rid of them and walked further, they followed him and knocked him down from behind. When he fell down, one of the assailants gave him a cut on his tongue, the statement said.
After the attackers drove away from the scene in a car, a passer-by helped the student to call an ambulance, which took him to a near-by hospital.
He was bleeding heavily from his head and from his mouth when the ambulance and police officials arrived at the scene, the statement said.
Police issued an appeal for help from eyewitnesses, who could provide vital clues to track down the two assailants.
