(Adds details on Hunter's tenure, shares)
July 31 (Reuters) - Molson Coors Brewing Co said on Wednesday U.S. unit head Gavin Hattersley will replace Chief Executive Officer Mark Hunter, who will retire in September after more than a decade with the brewer.
Under, Hunter, 56, the company bought out SABMiller's $12 billion stake in MillerCoors in 2016, which helped it grow sales in the United States.
But weakness in beer sales in the United States due to increased competition and growing demand for craft beers has weighed on the company's performance and its stock.
Its second-quarter sales fell 4.4% to $2.95 billion, well below Wall Street estimates, sending its shares down 8%.
Before becoming CEO in 2015, Hunter held several top positions and played a key role in the acquisition of the Carling business in the UK in 2002. Hattersley, 56, has been heading the U.S. unit since 2015 and was Molson's chief financial officer for three years before taking the role.
Reporting by Nivedita Balu in Bengaluru; Editing by Saumyadeb Chakrabarty and Arun Koyyur