Chirac, 72, was awake and consulting with advisers after being taken to Val-de-Grace Hospital in Paris on Friday evening, Prime Minister Dominique de Villepin said in the Atlantic coastal resort of La Baule.
"Last night, he had a small vascular incident causing slight vision trouble that should fade over the next few days," Villepin said of Chirac. "He will stay in hospital for a week."
Villepin did not offer more specifics, but a blood vessel problem of this type could range from a torn vessel to a stroke. Strokes are often connected with vision problems. More than 80 percent of strokes are caused by blockage in an artery carrying blood to the brain.
In a speech to members of Chirac's ruling conservative party meeting in La Baule, Villepin said he had found the president to be "in good form" when the two men spoke by phone Saturday morning.
Villepin said they discussed the government's agenda in coming days — in particular planned French aid for victims of Hurricane Katrina in the United States.
Villepin, in La Baule for a meeting of Chirac's ruling conservative party, said he would visit the president upon returning to the capital later Saturday.
Chirac's schedule had included the Franco-German summit Tuesday with German Chancellor Gerhard Schroeder and a lunch meeting with Prince Albert II of Monaco on Friday.
The presidential Elysee Palace said Chirac had discussed delaying his schedule with staffers and declined to comment beyond a hospital communique nearly identical to Villepin's statement.