The animal is said to have entered the house through a terrace door that was left ajar, the police in Wadern report.
When the homeowner tried to scare it away, the boar attacked him, knocking the man to the ground, setting about him with its tusks and trampling on him.
The man was taken to hospital with bite wounds and other injuries.
The incident took place in a side street in the middle of a district of Nonnweiler.
Following the attack, the wild boar ran off to the woodland and despite a search, police have not been able to track it down.
