The stabbing victim at the Damascus Gate of Jerusalem's Old City is a rabbi at the Ateret Kohanim Yeshiva in the Muslim Quarter.
A student walking with the rabbi fought off the attacker, preventing the attempted murder.
The rabbi was treated by Hatzala-Ichud medics and evacuated to Hadassah Ein Karem Hospital by Magen David Adom.
Police are searching for the stabber.