Errol Spence is "the real deal" and can beat Kell Brook if he executes his gameplan, Sugar Ray Leonard has warned.
Spence, 27, has a 21-0 record with 18 knockouts and will take on Brook for the IBF world welterweight title in the biggest test of his career at Bramall Lane on Saturday.
Brook has retained the belt three times, but heads into the bout on the back of a first career defeat after moving up two weight classes to take on middleweight king Gennady Golovkin.
Leonard, who was a champion in five divisions across a decorated career, believes Spence is the "whole package".
"Errol Spence Junior is the real deal from what I've seen, I've watched him from day one," Leonard said on Sky Sports.
"That's why I think the world is particularly excited about this fight with Kell Brook and Spence.
"Spence's assets are speed, poise, balance. He has the whole package and every time he gets into the ring he improves.
"The winner is the person who carries out their gameplan and doesn't get too cute."
Leonard also had praise for IBF and WBA world heavyweight champion Anthony Joshua after his sensational stoppage of Wladimir Klitschko at Wembley Stadium last month.
"Without question, they gave their heart. Joshua, so impressive, so resilient, it was spectacular," he said.
"When I ask my friends [in the United States] they love him. Joshua has the right personality, the right style, showmanship and power. He fights like a heavyweight."