With commissioner David Stern set to present Tim Duncan his fourth championship ring on Tuesday, the Spurs forward has made it clear he has no plans to leave the court ? or San Antonio ? anytime soon.

Duncan has reached agreement with the Spurs on a two-year, $40 million extension that figures to give the team enough salary-cap flexibility to continue to surround him with a competitive support cast in the waning seasons of his career, two sources with knowledge of the deal said Monday.

By signing the extension, which is expected to be finalized within the next few days, Duncan forfeits his option to become a free agent after this season. He will be under contract with the Spurs until the summer of 2012.