Hiroki Sakai (酒井 宏樹, Sakai Hiroki, born 12 April 1990) is a Japanese footballer. He currently plays for Marseille and the Japan national team.
Born in Kashiwa, Chiba, Japan, Sakai was introduced to football by his two older brothers and joined a school football team when he was the third grade of elementary school. He initially played as a striker before converting to a full back, a position he played today. Sakai spent 10 years with the school football team before joining Kashiwa Reysol U15 side in 2003.
Sakai progressed through the ranks of the Kashiwa Reysol and learned his guidance under Tatsuma Yoshida. Eventually, he worked his way through to the U16 and U18 side. During his progress, Sakai joined Mogimirin EC to study abroad on a short–term, though he said the experience benefited him to improve his right–back and centre–back positions, but returned to Japan in November 2009.