"It's tough for her," the team doctor René Tour tells Expressen. "Our physios are working non-stop."
The injury has been bothering Alshammar since early July. The 34-year-old, who took the gold medal at the World Championships last year, was aiming for an Olympic victory this year after earning two silver medals at past events.
The women's 50-metre freestyle event starts next Friday, 3 August.