WASHINGTON  — Secretary of State Hillary Rodham Clinton spent a second day at a New York hospital on Monday, under observation for a blood clot, stemming from a concussion she sustained while battling a stomach virus.

The illness has kept her out of the public view since Dec. 7, and has started to raise a host of questions as her team keeps typically tightlipped about the details.

Aides disclosed the blood clot Sunday, with her spokesman, Phillipe Reines, issuing a statement that said: “Her doctors will continue to assess her condition, including other issues associated with her concussion.” He had no immediate update Monday on her condition, raising the question of whether she will return to work before she steps down as secretary of state.