To lose the swede is a major blow against Swansea, writes the club on its website.
Olsson injured her left achilles tendon in Saturday’s match against Brentford. The match was stopped for eight minutes when the swede was oxygen, and he was carried out on a stretcher.
He has now undergone a successful operation, but the club write to other players with the same injury have taken between seven and nine months to come back.
He misses hence a large part of the EM-qualification, which for Sweden’s part kicks off against Romania and Norway, on 23 and 26 march.