The 21 year old looks like being the latest victim of the virus that has swept through Ewood Park, this is another setback for Olsson who has only managed six appearances so far this season.
"I have been noticing the symptoms for some time," Olsson told Swedish football site Fotbollskanalen.
"I spoke to some of the players a few days ago and told them how I felt and I have exactly the same symptoms as they have described.
"The club doctor also believes I have swine flu."