Keyshawn Johnson has filed a lawsuit against NFL agent Chris Ellison ... claiming the guy owes him nearly $1 million for helping funnel clients his way -- but Ellison is adamant the allegations are untrue.
Johnson said in his suit, which was filed in Los Angeles last week and obtained by TMZ Sports, that he and Ellison struck a deal about a decade ago ... in which the former New York Jets star agreed to push players to be represented by Ellison in exchange for a portion of the NFL contracts the athletes received.