Lil Wayne Investigated for Assault ... AGAIN

For the second time in a month, Lil Wayne and his entourage are under investigation for assault ... and once again the alleged victim caught a beatdown for daring to take a photo of Weezy.

Alfredo Marino tells TMZ on May 3 he spotted Lil Wayne and his posse skateboarding. Marino says he is a HUGE fan of Wayne's so he went up to Weezy to ask for a photo -- but was shut down.

Marino retreated to his car, where he tried sneaking a pic ... Marino claims Wayne walked over with his crew and began threatening him, saying, "Don’t you know all it takes is a word and these motherf**kers are going to f**k you up?"

Marino claims he was clocked from behind with a skateboard -- which knocked him down and left him bleeding from the head. Marino says he suffered a concussion and vertigo.

Marino's lawyer, Craig Chisvin, tells TMZ, "My client will enforce all of his rights under the law and all individuals responsible for this outrageous incident will be blamed for the damages that my client has suffered and continues to suffer."

In April, a photog in Miami filed a police report claiming he was attacked by Lil Wayne's crew for the same offense.