Sydney Thunder have suffered a major blow just weeks out from the start of their WBBL title defence with South Africa star Shabnim Ismail ruled out of the tournament with a knee injury.

Ismail missed the fifth and final ODI of South Africa's series against West Indies in the Caribbean having starred in the third match with figures of 3 for 31. But instead of heading to Australia to begin her quarantine period ahead of the WBBL, she will head home to South Africa to rehab her knee.

"She took a bad knock and unfortunately Shabnim won't be able to play in this season's WBBL competition," Thunder coach Trevor Griffin said. "It's terrible news because she's been an important member of Sydney Thunder over the last couple of seasons.

"She showed her class in the final against the Melbourne Stars at North Sydney Oval last year. I'm just as disappointed for her because I know how much she enjoys being a part of...the WBBL."

Ismail was Player of the Final last season knocking over Melbourne Stars duo Elyse Villani and Meg Lanning to help Thunder claim the title. Thunder are also without English duo Heather Knight and Tammy Beaumont who were unavailable despite England's tour of Pakistan being cancelled.

They have managed to find two excellent replacements signing India duo Smriti Mandhana and Deepti Sharma.

Meanwhile, India team-mates Shafali Verma and Radha Yadav have signed with cross-town rivals Sydney Sixers.

The WBBL begins on October 14, following India's ongoing multi-format series against Australia, with the first 20 matches to be played in Tasmania.