Isaac was the captain of Nigeria under-23 squad for the 2008 Summer Olympics, held in China.

On 13 August 2008 at Tianjin Olympic Center in Tianjin, Isaac scored Nigeria’s first goal against the United States in the preliminary stage, Nigeria went ahead to win the match by 2–1.

Nigeria won Group B in the preliminary stage, also beating Japan, and drawing with the Netherlands. They defeated Ivory Coast and Belgium in the knockout stage, before losing to Argentina, 1–0, in the Gold medal match, earning the Silver medal.

Isaac first appeared on the senior squad for Nigeria in 2009. He earned 3 caps, and scored one goal.

He played professionally for 14 seasons, much of which was spent in Turkey. He scored a total of 77 club goals during his career.