The student, whose identity has not been revealed, is recovering well and his injuries are not as serious as thought initially, a police spokesman told PTI.
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 refused, 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.