Rick Macci -- the iconic coach who helped Serena Williams become a household name -- says he's happy the tennis superstar is walking away from the sport on her own terms ... telling TMZ Sports he's not surprised by her decision.
Of course, the former player and coach played an important role in shaping both Serena and Venus' careers ... teaching the sisters in their youth as they became the best sister duo in the world.
We spoke with Macci about Serena's recent retirement announcement ... and he says he wasn't shocked by the news.