Former US President George H W Bush is in intensive care with a fever in a Texas hospital.
His spokesman said Mr Bush was transferred to the intensive care unit on Sunday after suffering a series of setbacks.
The 88-year-old was initially admitted to hospital for treatment for bronchitis on 23 November.
He is the oldest living former president and a Second World War veteran.
Mr Bush, the 41st US president and a Republican, took office in 1989 and served one term in the White House.
The father of former President George W Bush, he also served as a congressman, as ambassador to the United Nations, as envoy to China, as CIA director and as vice-president for two terms under Ronald Reagan.