The one-man search party was 39-year-old Kevin Villegas (left) -- who worked as an assistant for Nic Cage for the past 5 years. We're told Kevin's primary responsibility was looking after Weston.
But Tuesday, when Weston went M.I.A -- sources tell us Nic dispatched Kevin to track down the 21-year-old and bring him home. Kevin quickly located his target in L.A., but we're told, Weston was resistant and aggressive -- even threatening to rip off Kevin's "Christian f**king head."
Sources tell us Kevin immediately reported the situation to Nic ... who instructed Kevin to call 911. When Weston realized cops were on the way he flipped out and attacked Kevin with the roundhouse kick.
We're told Kevin -- who served with the U.S. military -- feared for his life because Weston is a highly-trained fighter ... and attacked Cage with a flurry of punches.
Cops came and Weston was hospitalized for a mental evaluation. Weston says he may press charges.