Club Attack Arrest

According to law enforcement sources, the unidentified suspect -- said to be in his 30s -- was arrested this morning in his L.A. home on suspicion of felony assault ... and is currently being held on $500,000 bail.

Shocker ... law enforcement tells us, alcohol played a key role in the incident outside the Roxbury nightclub -- when the attacker delivered a devastating punch to the head of a man who had just walked out of the club.