A police spokesman in the southwestern city of Wroclaw, said the attacker approached Fr Ireneusz Bakalarczyk on Monday morning in front of the city's Holiest Mary church.
Polish news site TVP.info reported that the man spoke to the priest, who was on his way inside the church, before suddenly stabbing him in the chest.
The attacker has been detained.
A spokeswoman for Wroclaw Univesrity Hospital said the priest has undergone surgery for chest wounds and is in stable condition.
A motive remains unclear.​
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