Defending champions England and the Black Caps will begin the 45-day showpiece tournament at Ahmedabad's 130,000-capacity stadium on Thursday.
"He (Stokes) has got a slight niggle in his hip. Fingers crossed that it'll be good news for us," Buttler told reporters.
"He is working hard with the physios and we'll know more when the guys arrive for training today. We'll make the right call: if he's not fit to play, he's not fit to play.
‘Not the time for risks’
He added: "It's not the time to take big risks at the start of the tournament. It's going to be a long tournament.”
The 32-year-old Stokes was selected for the World Cup as a specialist batsman after a long-standing knee injury ruled out his role as a bowler.
Harry Brook could be included in the team for his seventh ODI since his 50-over debut in January if Stokes misses out.
Buttler praised the swashbuckling batsman.
"He's not played loads of ODI cricket, but it's a format that should suit him perfectly. It will allow him to bat for a long time and make big runs and that's something he enjoys doing.”
Thursday's game will be a rematch of the 2019 final at Lord's which was decided on boundary countback after the scores were level after a super over.
England won the latest ODI series between the two sides at home 3-1 in September.
It was in that series that Stokes struck the highest score by an England batsman in a one-day international, his 182 setting up a thrashing of New Zealand at The Oval.
Buttler said the 2019 World Cup final win -- under Eoin Morgan -- will not have a bearing on Thursday.
"No, I don't. Four years ago is a long time," said Buttler.
"It was a fantastic match with New Zealand and we've had some fantastic games against them. They're an excellent team. We expect a really tough match and we're excited for the first match of the World Cup.”
Buttler, who led the team to a T20 World Cup title last year, said there is no added pressure of being the first England captain to defend their ODI title.
"I think I've spoken quite a bit about not feeling like we're defending anything," said Buttler.
"We're here very much in the same position now as every other team. We're here to try and win the World Cup. We're all starting in the same place and have big dreams and ambitions of going all the way."