Australia batsman Usman Khawaja has been ruled out for up to nine months with a knee injury.
Khawaja will need surgery to repair a torn anterior cruciate ligament after suffering the injury while catching a ball in a training session with the Sydney Thunder.
The 27-year-old has fallen out of favour with the Australian selectors, and the setback means that he will be unable to win back his place for the Ashes series in England next year.
"We are very disappointed that Usman will not be taking the field for us this summer and we wish him well with his recovery," Sydney Thunder general manager Nick Cummins said. "While his presence in the middle will be missed, he will remain with the Thunder and continue to contribute to the team with an off-field role.
"At this stage we will not be replacing Usman in the squad. We are confident in the group of batsmen we have assembled and look forward to seeing one of our younger players step up to fill his place."
The Thunder begin their Big Bash campaign against the Brisbane Heat on Sunday.
