With Trabzonspor, he scored two goals in 26 macthes. Because of his average performans he was loaned out to Manisaspor for a year. Isaac played 27 matches and scored six goals. In the summer of 2010, Manisaspor signed a contract with Isaac. After scoring 11 goals in 30 matches with his now relegated club Manisaspor, he signed a 3-year contract with Antalyaspor.
Isaac was named as the captain of Nigeria squad for the 2008 Summer Olympics. On 13 August 2008 at Tianjin Olympic Centre Stadium of China, Promise scored Nigeria's first goal against USA in the preliminary stage, Nigeria went ahead to win the match by 2–1.