New Zealand's hopes of winning a second straight Netball World Cup have suffered a massive blow with star shooter Grace Nweke ruled out of the remainder of the tournament with a knee injury.

The 21-year-old limped off in the third quarter of the Silver Ferns' 80-19 victory over Singapore in Cape Town on Sunday.

It was initially expected she would only miss Monday's match against Wales, but New Zealand Netball had their worst fears confirmed.

"Absolutely devastating news to share that shooter Grace Nweke has been ruled out of the Netball World Cup after scans today confirmed a partial tear in her patella tendon," the national body said in a statement on social media.

"Travelling reserve Tiana Metuarau has been called into the playing 12 for the remainder of the tournament."

Nweke has been almost unstoppable in the early stages, scoring 31 from 31 attempts against Trinidad and Tobago, and 15 from 16 against Uganda.

Diamonds great Catherine Cox said her absence meant the Kiwis wouldn't successfully defend the crown they won from Australia in 2019.

New Zealand won that final over the Diamonds by one goal.

"The very short answer is no they can't (win without her)," Cox told Kayo sport.

Metuarau, 22, is 10cm shorter than Nweke, so Cox predicted New Zealand would turn to veteran Te Paea Selby-Rickit and Maia Wilson, who would fill the goal shooter bib.

Metuarau's mother is Wai Taumaunu, who played 68 Tests for New Zealand and is a former head coach of the Silver Ferns.

"Metuarau comes from great pedigree. She knows the game inside and out, but what a moment for a 22-year-old who thought she was there to support the Silver Ferns thrown into the mix," commentator Cox said.