The Georgia Democrat will be traveling out of the country until Monday, his spokeswoman said Thursday. Obama is scheduled to appear with his running mate on Saturday in Springfield, Ill.
Cathy Gwin, Nunn's spokeswoman at the Nuclear Threat Initiative, declined to offer details of Nunn's trip but said he was traveling on international business.
Nunn's name has been circulated recently as a possible running mate for Obama. He was widely viewed as the Senate's foremost authority on foreign affairs when he retired from the Senate in 1996. He remains active in international affairs, including as CEO of the Nuclear Threat Initiative, a Washington-based group fighting nuclear proliferation.