Jay-Z -- NFL to Investigate Signing of Geno Smith

Jay-Z's foray into sports management has already hit a snag -- the NFL is investigating whether the rap superstar violated league rules involving the recruitment of New York Jets draft pick Geno Smith.

Jigga's Roc Nation Sports signed Smith earlier this week and a photo of Smith with Jay-Z was posted to Instagram prior to the announcement. The problem is ... league rules mandate that only NFLPA-certified agents may be involved in the recruitment of clients.

Also complicating matters ... Smith's adviser, John Thornton, was quoted as saying he was in meetings with Smith and Jay-Z, but later said he was misquoted.