The attack happened during a robbery at a house in Cawnpore Street, in the Clonard District of west Belfast last night.
Two men entered the house just after 10 pm and attacked a man with a pocket knife.
Another man who was in the house at the time was not injured.
Two mobile phones were stolen.
The attacked happened as church goers were leaving the Novena at Clonard Monastery.
The PSNI launched its helicopter last night in a bid to catch the attackers.