Madushanka was seen limping away from training on Saturday and was quickly sent for an MRI which confirmed the injury.
After making his international debut in the recent Asia Cup, Madushanka had impressed during the tournament, taking six wickets and maintaining an economy rate of 7.75 over six matches.
Bringing lively pace and swing to the powerplay overs, as well as variety at the death, he might have become Sri Lanka’s second choice quickly, behind Dushmantha Chameera. He is 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 will have to play the first round of the World Cup, where they will play the UAE and the Netherlands in addition to Namibia, to qualify for the main draw.