3 People Who Could Replace Outgoing Defense Secretary Chuck Hagel

Ashton Carter, Michele Flournoy and Sen. Jack Reed will likely be considered.

Obama's nominee will likely come from this list:

quicklist:1 title: Ashton Carter, Former Deputy Defense Secretary media: 27137414 text: Dr. Ashton Carter served as the Deputy Defense Secretary from October 2011 to December 2013, where he oversaw military budgeting during a troubling financial time for the department.

He also served in the Clinton administration as Assistant Secretary of Defense for International Security Policy.

In 2012, she stepped down from her Defense Department position to become a national security adviser on Obama's re-election campaign. She later joined the Boston Consulting Group as a senior adviser to the public sector.

Flournoy earned a bachelor’s degree in social studies from Harvard University and a master’s degree in international relations from Balliol College at the University of Oxford.

Prior to his election to the Senate in 1996, Reed served three terms in Rhode Island's State Senate and three terms in the U.S. House. After his graduation from West Point in 1971, he received an active duty commission in the Army, and earned a master's degree in public policy and later, a law degree from Harvard.

Though Reed's name has been floated as a potential replacement, Reed's spokesperson says the Senator "does not wish to be considered" for the Secretary of Defense or any other Cabinet position.

"Senator Reed loves his job and wants to continue serving the people of Rhode Island in the United States Senate," said Reed's Press Secretary, Chip Unruh. "He has made it very clear that he does not wish to be considered for Secretary of Defense or any other cabinet position. He just asked the people of Rhode Island to hire him for another six year term and plans on honoring that commitment."

ABC News' Jonathan Karl and Arlette Saenz contributed to this report.