The victim was identified as Assistant Sub-inspector Abdul Mannan of Detective Branch of Police.
The team, however, managed to detain the culprit identified as Md. Salim, said Saiful Alam, officer-in-charge of Sylhet district DB Police.
Police sources said a team of detectives headed by Sub-inspector Abdul Mannan conducted a drive at the place in the afternoon and caught Salim red-handed while he was selling drugs.
Later, Salim untied himself from the police grip during a scuffle and fled away. At one stage, Salim took a 'Da' (sharp weapon) from the kitchen of a nearby house and stabbed the cop, leaving Mannan severely injured.
The injured was taken to Jaintapur Health Complex for treatment, said the OC.