The princess has cancelled a planned trip to Finland later this month, where she was to meet the country's President Sauli Niinistö.
"This is a continuing challenge for the Crown Princess, and it can not be excluded that the period will be extended," her press officer Marianne Hagen said. "The Crown Princess will still attempt to attend some events during the period."
The Princess has had neck and back problems ever since tripping up and knocking her head on a cobblestoned street during a visit to the Ukraine in 2008. The accident left her with serious concussion, causing most of the trip to be cancelled.
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In 2010, the Crown Princess missed the Olympics in Vancouver when the neck problem recurred.