"The assailant man slashed her across the back twice with a razor knife and glared at her face before leaving the bus," Deshapriya said.
"She is in shock."
The lady librarian had been visible in video images broadcast of an incident where media workers held junior labour minister Mervyn Silva hostage after he assaulted the news chief of the state-run Sri Lanka Rupavahini Corporation.
The news chief has since been transferred to a different division.
A number of media workers who covered the incident and spoke out has been assaulted or threatened by unknown persons.
No action had been taken against the errant minister, but up to 20 journalists had been question by the island's secret police.
"Attacks and acts of intimidation against journalists for objecting to Silva's use of force are intolerable," Re