DeSean Jackson -- Drew Rosenhaus Bribed Me with Cash ... and Louis Vuitton

DeSean Jackson says his former agent Drew Rosenhaus violated NFL Player's Association rules by bribing him to sign with his agency back in 2009 with truckloads of cash and a Louis Vuitton bag ... this according to legal docs obtained by TMZ Sports.

Jackson filed new court papers in an effort to overturn an arbitrator's ruling that he owes Rosenhaus more than $500k for failing to repay loans.

In the docs, DeSean says he shouldn't have to pay Drew a dime because a huge chunk of the cash was given to him to induce DeSean to use D.R. in his next contract negotiation.

Why is that a big deal? Because according to DeSean, it's a huge violation of NFLPA rules -- for which the NFLPA punishment is that DeSean wouldn't have to repay a single cent.

Now for the cool part ... part of the money he received from Drew came IN CASH -- stuffed inside a Louis Vuitton bag he received just after midnight on Nov. 10, 2009.

No word if he kept the bag ... but c'mon, it's Louis.