Cassano was forced off during Inter's 4-3 defeat at home to Atalanta on Sunday, with the club subsequently confirming that he had sustained a grade two hamstring strain.
It is thought the 30-year-old will miss at least the next four weeks.
"Cassano underwent a series for tests after being forced off in the first half of last night's match against Atalanta," said a club statement on their official website.
"The scans revealed that the striker has suffered a grade two hamstring strain."
The news deals a blow to Inter's hopes of qualifying for next season's UEFA Champions League.
Sunday's defeat left them eight points adrift of third place in Serie A, currently occupied by local rivals AC Milan, with seven games remaining.
Inter's top scorer for the season, Rodrigo Palacio, is currently out of action with a thigh problem while fellow striker Diego Milito was ruled out for the season in February with a cruciate knee ligament injury.