St. Louis Rams Rookie SUED -- I Got You Tailor-Made Suits ... and You Screwed Me!

St. Louis Rams rookie Robert Quinn was LOOKIN' SHARP after he was picked 14th overall at the 2011 NFL Draft ... but now the guy who allegedly hooked up his fancy threads is suing ... TMZ has learned.

No, we're not talking about Quinn's tailor ... the dude with the beef is an agent who claims he repped Quinn during the draft ... but was kicked to the curb right before Quinn signed his MASSIVE $9.4 million contract.

According to a new lawsuit obtained by TMZ ... Carl Carey claims he signed a deal with Quinn when the former University of North Carolina defensive end decided to turn pro.

Carey claims Quinn was viewed by NFL teams as a guy with some serious "character flaws and health concerns" ... until Carey reconstructed his image.

In the lawsuit, filed in federal court in North Carolina, Carey claims he did EVERYTHING for Quinn ... including party-planning, media training, and even "arranging for tailor-made suits."

Quinn also claims he negotiated deals with Nike and trading card companies.

But just before Quinn signed his contract ... (months after the draft) ... Carey claims he was fired ... and has not received the 3% cut he was contractually obligated to receive.