Lindblom, 23, will undergo further testing and evaluation next week and then begin treatment. The cancer was diagnosed by specialists at the University of Pennsylvania.
Ewing's sarcoma grows in the bones, or around the soft tissue around the bones. It primarily affects children and young adults.
The Flyers said they "will do everything possible to support Oskar and assist him in securing the best care available."
Lindblom has 11 goals and seven assists in 30 games with the Flyers this season; he is tied with Travis Konecny for the team lead in goals. Lindblom missed the Flyers' last game with what the team called an upper-body injury.
He had 17 goals and 16 assists last season, his first full campaign in the NHL. Lindblom, a native of Sweden, has 30 goals and 27 assists in 134 career games, all with the Flyers, who drafted him No. 138 overall in 2014.