Hagel told CBS' "Face the Nation" Sunday he expected Afghan President Hamid Karzai to eventually end his holdout and sign the new agreement; however if he did not, the possibility existed of a complete U.S. exit from the country.
"It is a very real possibility because if we don't have a bilateral security agreement...that means we can't protect our forces that would be here after 2014," Hagel said. "Afghanistan essentially will be alone, but we have no other options."
Karzai stunned the United States last month when he announced he would not sign off on the new deal despite its non-binding endorsement by a national assembly known as a Loya Jirga. Karzai called for further negotiations and insisted he would not sign until after next year's Afghan presidential elections.
Hagel, who made an unannounced visit to Kabul this weekend, said Karzai's move had not been anticipated but refused to say Karzai was not a reliable partner. "Yes, it was disappointing and yes it was surprising but we are dealing with the realities that we have before us," he said.