Social Democratic Party leader Antti Rinne's sick leave is set to last until late February – just over a month before voting begins in the parliamentary election. The SDP, the largest opposition group in Parliament, has consistently led in public opinion polls over the past six months.
The party had expected him to return to politics in late January. On Monday Rinne announced on Facebook that his leave now will probably last until late February.
Rinne is being treated for pneumonia at a hospital in Helsinki, where he was also found to have a hospital superbug caught in Spain.
The SDP chief and his wife were hospitalised with respiratory illnesses around New Year's while on holiday in Spain.
According to the tabloid Iltalehti, Rinne's treatment there "did not progress as planned". The paper says his "situation became very serious" and he was medevacked back to Helsinki on 11 January.
Marin standing in at campaign events
In his Facebook post, Rinne said that "besides serious pneumonia, another health problem cropped up at the same time, coronary artery disease... And along with everything else, I found out that I had also acquired hospital infection in Spain."
He added that doctors estimate that his sick leave will last until the end of February – less than five weeks before advance voting begins on April 3.
So far during Rinne's sick leave, he has been replaced at election debates and other events by deputy chair Sanna Marin.
Rinne, 56, a former finance minister, union boss and labour lawyer, has led the SDP for nearly five years.