England captain Jos Buttler accepted Chris Woakes's form with the new ball was a major concern heading into the faltering champions' key World Cup clash against South Africa on Saturday.

England's title defence in India is in deep trouble after a shock defeat by Afghanistan left them with a single win to their name.

Woakes has taken just two wickets across England's first three games at a hugely expensive average of 67.5

The 34-year-old seam-bowling allrounder has struggled to make an impact on Indian pitches and went wicketless during a stunning 69-run loss to Afghanistan in Delhi on Sunday.

"He's been a fantastic performer for an incredibly long time for England in all the formats and especially in one-day cricket," said Buttler of Woakes during a pre-match press conference in Mumbai on Friday.

"And we're all honest guys, right? We're all honest professionals who hold each other to high standards and individually expect a lot of ourselves. He knows he's not performing quite how he would like to at the minute and that's frustrating."

With Ben Stokes declaring himself fit for the first time this tournament following a hip problem, someone will have to make way.

But Buttler was at pains to stress the axe had yet to fall on Woakes, a veteran of 117 one-day internationals.

"We always back all our players that are in our team – we picked them for a number of reasons and one because they're high-class players and he (Woakes) is certainly one of those."

Turning to test captain Stokes, one of the stars of England's 2019 World Cup triumph, Buttler said: "Ben trained really well last night. It's great to see him back.

"He obviously brings a lot on the field and with his presence and leadership skills as well as someone who is always good to turn to."

South Africa too will arrive at the Wankhede Stadium on the back of an embarrassing loss following a 38-run defeat by the Netherlands, the non-test nation inflicting fresh pain on the Proteas after knocking them out of last year's Twenty20 World Cup in Australia.

Buttler, having lauded South Africa's "strong top six" and fast-bowling depth, admitted he had been as taken aback as anyone by Tuesday's result in Dharamsala.

"I think you're always surprised when those kind of things happen," he said.

"No disrespect to the Netherlands. They played a fantastic game of cricket and deserved to win it...But that's why sport is fantastic. It throws up these upsets."