Madushanka was seen hobbling away from practice on Saturday and was soon sent to get an MRI scan, which confirmed the injury.
Having made his international debut in the recent Asia Cup, Madushanka had impressed through the course of the tournament, taking six wickets and maintaining an economy rate of 7.75 across six matches.
Having brought lively pace and swing to the powerplay overs, as well as variety at the death, he had perhaps become Sri Lanka’s second-choice quick, after Dushmantha Chameera. He was likely to be in the XI for Sunday’s first-round match against Namibia.
The other seamers in the Sri Lanka squad are Lahiru Kumara and Pramod Madushan.
Despite their recent Asia Cup victory, Sri Lanka must play the first round of the World Cup, where they play UAE and Netherlands in addition to Namibia, in order to qualify for the main draw.