Kenyan-born Danish athlete Wilson Kipketer has been hospitalised since Monday in Faro, Portugal, according to a statement released on Friday by the Danish Federation.
Kipketer (24) is the reigning 800m world champion and holds the world records indoors and outdoors in the 800m, after demolishing Sebastian Coe's longstanding record twice in the course of 1997.
Kipketer has since received major accolades from around the world, notably being named Athlete of the Year by the International Athletic Foundation and by Reuters.
He is one of three candidates for this year's Jesse Owens award.
Kipketer was training in Portugal and it is understood that doctors have recommended that he continue to receive treatment in Faro for the time being.