The 24-year-old, who captains Swiss club Young Boys Bern and plays for the Switzerland women’s national team, disappeared Saturday afternoon on Lake Como in Lombardy.
While the club said she'd been swimming, the Italian news agency Ansa reported that she dove off of a boat she'd rented with a friend and never resurfaced, according to The Associated Press.
Club officials said they were in contact with Ismaili’s family and will issue an update when more information becomes available.
Ismaili has played for Young Boys since 2011. She made her debut with the senior national team in 2014.
The Associated Press contributed to this report.