The sergeant allegedly beat a suspect who was in custody earlier this week.
Weis made the announcement during an unusual Friday evening news conference. He gave very little information.
ABC7 has learned of an incident involving a young man at a drinking party at a building in the South Loop. However, the superintendent declined to answer questions or give out any details.
"I will not, nor will I ever, tolerate brutality against the very people that we have taken an oath to serve and protect," said Weis.
The superintendent said he has no tolerance for police misconduct, which is why he immediately stripped a sergeant of his police powers Friday after he learned of the misconduct allegations.
Weis says he was notified Friday by the Independent Police Review Authority that they were investigating the incident, but because the matter is still under investigation, Weis declined to identify the officer, the alleged victim, or the police district where the alleged incident happened.
The superintendent has been criticized by the rank and file for his handling of other high-profile police misconduct cases, including that of Anthony Abbate, who was taped repeatedly striking a female bartender.
Weis said the current investigation could still include others people.
"If members are found to have neglected action or to have failed to report the incident, appropriate and swift action will be taken," said Weis.
A spokesperson from the Independent Police Review Authority confirmed they are investigating this case. However, he said it would be irresponsible to discuss any aspect of it.