Williamson suffered the knee injury fielding in the Indian Premier League at the end of March and was immediately ruled out of the tournament, which starts in India a month today.
However, the 32-year-old is on track to make a faster-than-expected recovery and has been training with the squad during the tour of England, which continues this evening with the Fourth T20 at Trent Bridge.
While there is still no date being put on his return to action, head coach Gary Stead last night revealed his captain will be in the 15-man squad to be named on Monday. The World Cup lasts more than seven weeks and Williamson could play a part later in the tournament, even if he is not fit for the opener against England on October 5.
Stead confirmed that the batter will still have to show signs of progress over the next three weeks, with teams allowed to tinker with their squads until late this month, but his availability would be a major boost to the Black Caps, whose batting has looked fragile on their tour of England.
Tim Southee's side were hammered in the first two T20s, before fighting back with an emphatic 74-run victory at Edgbaston on Sunday, though that win came against a heavily rotated England attack.
The start of a four-match ODI series in Cardiff on Friday will see the returns of a host of players who led England to World Cup glory against New Zealand in 2019, including Joe Root, Chris Woakes, Mark Wood and the un-retired Ben Stokes.
Opening batter Jason Roy said last week that he expected a significant changing of the guard to follow England's attempt to defend their title, and speaking ahead of tonight's T20 in Nottingham, Moeen Ali agreed that the prospect of a last hurrah is part of this side's motivation heading to India.
"A lot can happen still, but I think not just for England, for most countries, there are a lot of players in their mid-thirties who might just think about retiring after the World Cup," he said.
"I've not really fully thought about it [retiring from ODIs], but it potentially could be, yeah."