A forecast for rain has added an unknown element to New Zealand's final World Cup group stage match against Sri Lanka in Chennai on Thursday, captain Kane Williamson said.

New Zealand occupy the last semi-final slot available but only by virtue of having a better net run rate than Pakistan and Afghanistan, with all three teams tied on eight points after eight games.

"We'll still have to very much see what the pitch is like. There's been a lot of weather around and it could look different tomorrow," said Williamson.

"There's lots of things that we can't control and the weather is one of those. There may be a thought in the back of your mind, but at the end of the day, our focus will be on the cricket that we want to play."

New Zealand, finalists in 2019, won their first four matches in India before losing the next four.

"There were also some really close games and ones that we lost," Williamson said.

"I think if we look at the cricket on a whole, there has been a lot of good cricket.

"The beauty of this type of layout is that you do play everybody, you are challenged by everybody in different ways, so the focus is much more about your own cricket and how you look to try and handle that."

New Zealand similarly struggled to make the semis in 2019 but were able to turn things around and reach the final.

"I suppose guys have had some of those experiences, but it's another game on another day and four years later," Williamson said.

"So, the focus is here and now and on the conditions, and how we want to adjust."

Williamson added that pacer Lockie Ferguson's return after missing two matches due to injury would depend on pitch conditions.