Ford, 92, was admitted to Eisenhower Medical Center, near his home in the California desert, on Jan. 14. He was initially expected to be released five days later.
"The doctors are assessing him for discharge on a day-to-day basis," his chief of staff, Penny Circle, said in a statement. "He's not quite ready for release from the hospital."
His condition is not life-threatening, she said.
The nation's oldest living former president was hospitalized briefly last month for routine tests. At the time, he had a bad cold.
Ford, a Republican from west Michigan, had a minor stroke during the 2000 Republican National Convention and was hospitalized after a dizzy spell on a golf course in 2003.
He and his wife, Betty, have lived in Rancho Mirage since leaving the White House in 1977.