After Brazilian newspaper Valor Economico reported Amazon (AMZN) may make its long-awaited launch into the Brazilian e-commerce market within the week, shares of MercadoLibre (MELI) are sliding in early trading.

Goldman Sachs analyst Irma Sgarz said a successful launch by the e-commerce giant could negatively impact the market share and gross merchandise volume growth of incumbents, such as MercadoLibre, while also forcing them to invest more heavily in free shipping and seller services. MercadoLibre has significant GMV exposure to electronics and Netshoes (NETS) could also be exposed if Amazon enters the markets of apparel and sporting goods, added Sgarz.

PRICE ACTION: In morning trading, MercadoLibre shares are down over 6% to $256.94 while Netshoes is down more than 2% to $12.57.