A Roberto Clemente rookie card -- one of the greatest outfielders in MLB history -- is hitting the auction block next month ... and is expected to sell for over $1,000,000!!
TMZ Sports has learned Clemente's 1955 Topps rookie card -- recently graded a PSA 9, indicating "mint" condition -- will go up for auction in September, and could rival the previous record for a Clemente card, $1.107 million.
PWCC officials tell us the '55 Clemente rookie card is in the "upper echelon of quality for vintage trading cards.