French First Lady Valerie Trierweiler is staying in hospital in Paris, where she has been since a magazine accused President Francois Hollande of having an affair.
She had been expected to leave hospital on Monday, but her aides said doctors had told her she needed more rest.
Ms Trierweiler went into hospital on Friday shortly after Closer magazine reported Mr Hollande was having an affair with actress Julie Gayet.
"She needs to recover from the shock she has suffered," an aide told Europe 1 on Monday.
Mr Hollande did not deny the report but protested at invasion of his privacy.
The BBC reports the president and Ms Trierweiler have been together since 2007.
Le Parisien newspaper quoted one of her friends as saying she is willing to forgive Mr Hollande, but wants to know about his intentions as soon as possible.
Mr Hollande, who has never married, left his previous partner, fellow Socialist politician Segolene Royal, to be with Ms Trierweiler. He and Ms Royale have four children; they were together for about three decades.
Ms Trierweiler, 48, moved in with Mr Hollande after his official separation from Ms Royal in 2007, and was divorced from her own husband, with whom she has three children.