Oklahoma City forward Serge Ibaka has reached agreement on a four-year, $40-million plus contract extension, league sources told Yahoo! Sports.

Ibaka, 22, could’ve been a restricted free agent next summer, and his deal now locks into place three of the Thunder’s core young stars — Kevin Durant, Russell Westbrook and Ibaka.

This deal leaves the future uncertain for guard James Harden, who could command a maximum contract on the league market as a restricted free agent next summer. Along with the remainder of Kendrick Perkins three years and $27 million, the small-market Thunder will be hard-pressed to invest so much money into his payroll.

In his third NBA season in 2011-’12, Ibaka averaged 9.5 points, 7.5 rebounds and 3.6 blocks per game. He’s one of the league’s best rim protectors, and been rapidly developing his offensive game. Ibaka was a key player on Spain’s silver medal winning Olympic team this month in London.

via Yahoo! Sports