Sources told Daily Trust that Mrs. Jonathan left Abuja a week ago to a German hospital to treat an undisclosed condition.
The First Lady, whose local and foreign trips normally enjoy wide coverage in state-run media, travelled out on Monday with no official announcement of where she was headed.
But her absence at public events has been conspicuous.
During the past week, Mrs. Jonathan, 55, has not been seen at any public function.
She has not accompanied President Jonathan on his trip to Addis Ababa for the funeral yesterday of the late Ethiopian Prime Minister Meles Zenawi.
Mrs. Jonathan was not with her husband in Anambra State on Thursday where he launched the Orient Petroleum facility.
Also, she did not join the president on his two-day trip to Senegal on August 22. The last foreign trip the First Lady embarked on with the President was to Trinidad and Tobago at the beginning of last month, few days after she hosted the African First Ladies Summit in Abuja.
A source at the weekend said Mrs. Jonathan has gone to a hospital called Horst Schmidt Klinik in Wiesbaden, Germany, but did not say what condition she went there to treat.
Horst Schmidt Klinik is where the late President Yar’Adua was once hospitalised for kidney-related ailments.
But the office of the First Lady said last night that Mrs. Jonathan’s foreign trip was “to take time off to rest” and not for medical purposes.
First Lady’s spokesman Ayo Osinlu confirmed that Mrs. Jonathan has travelled abroad since last week but that she was only away to take a “moment’s rest” given that she has not taken a rest since President Jonathan’s election last year.
Osinlu told Daily Trust by telephone that after the African First Ladies Summit which she hosted late July, Mrs. Jonathan decided she should take some time off to rest.
“If you look at her itinerary in August, you will be wondering how she was able to accomplish that,” Osinlu said.
Asked when the First Lady is expected to return to Nigeria, Osinlu said, “In the course of this week she will be back home. But remember, it all depends on her plans.”
He added that she may decide to extend her stay abroad.
The Dr. Horst Schmidt Hospital Corporation is the Municipal Hospital of the city of Wiesbaden, according to its website. It serves as a teaching hospital for the University Medical Center.
“With 21 clinics, four institutes and 1027 beds we offer our patients a very sophisticated and high-quality treatment range for the necessary care in our region,” information on the website said.
The hospital says it has more than 3000 workers.