When spectators bought tickets for the one-day tournament, they were asked to specify a team preference by the International Cricket Council (ICC).
Of those that did for the Cardiff semi-final, 30 percent said they were India fans.
But with title-holders India playing Bangladesh in Thursday's second semi-final at Edgbaston, there are concerns that Wednesday's match at the 14,100 capacity Cardiff ground could be blighted by mass no shows.
The deadline for fans to get their tickets on the resale site is midnight (2300 GMT) on Tuesday and after that officials will decide whether they can put them on sale on the morning of the game.
Both semi-finals are officially sold out.
But some 8,000 fans have gone 'missing' from the three group fixtures played in Cardiff.
"That's been reasonably disappointing here, but we are doing as much as we can across all of our channels," Claire Furlong, the ICC's communications manager, told reporters at the ground on Tuesday.
"It is a sell-out but we are doing as much as we can to ensure it's a sell-out with bums on seats as well," she added.
There were suggestions bad weather may have been a factor in people deciding not to turn up on the day for England's match against New Zealand in Cardiff.
But Eoin Morgan, the England captain, was confident of plenty of support on Wednesday.
"Cardiff has always been a very good venue for us and the last game we had great support and a full house and everybody seems to get right behind us," he said.
"I think tomorrow is sold out. That is what I have been told."
SQUADS: England Team: Jason Roy, Alex Hales, Joe Root, Eoin Morgan(c), Ben Stokes, Jos Buttler(wk), Moeen Ali, Steven Finn, Liam Plunkett, Mark Wood, Jake Ball, Jonny Bairstow, Sam Billings, Adil Rashid, David Willey
Pakistan Team: Sarfraz Khan (c and wk), Ahmed Shehzad, Azhar Ali, Babar Azam, Faheem Ashraf, Fakhar Zaman, Haris Sohail, Hasan Ali, Imad Wasim, Junaid Khan, Mohammed Amir, Mohammed Hafeez, Shadab Khan and Shoaib Malik.
Ben Stokeschampions trophy 2017England vs Pakistanicc champions trophyindia vs bangladeshJoe RootLive Cricket Scorelive scoreMS DhoniSarfraz Ahmedshakib al hasanvirat kohli
First Published: June 14, 2017, 9:42 AM IST