England opt to bowl against India in must-win Cricket World Cup game
The defending champions have lost four of their five matches and come in unchanged at Lucknow's Ekana Stadium in hunt of victory to cling on to their slim hopes of making the semi-finals.
England's last loss was a crushing-eight wicket defeat to Sri Lanka after they folded for 156.
"We haven't done ourselves justice," admitted Buttler.
Rohit Sharma's India remain the team to beat with five wins in as many matches and come in with the same team that beat New Zealand last week.
Home fans at the stadium believe a win over England is a foregone conclusion.
"India is going to bash England today left, right and centre," Roi Shaunauk, 29, told AFP.
Shaunauk said he came in the hope that Virat Kohli would equal all-time great Sachin Tendulkar's ODI record of 49 centuries and become "the best".
Indian players are wearing black armbands in tribute to Bishan Singh Bedi, a former captain and spin great who died October 23 aged 77.
England's dismal campaign has left them bottom of the table behind even The Netherlands and one of their small coterie of supporters in Lucknow laughed when asked about their chances.
"I've been wanting to come to India for a long time and the opportunity to see England play was a bonus," said Alex Piper, 32, on a two-week trip to the country with friends.
"Unfortunately, it's not worked out so well for us."
Teams
India: Rohit Sharma (capt), Shubman Gill, Virat Kohli, Shreyas Iyer, KL Rahul (wk), Suryakumar Yadav, Ravindra Jadeja, Kuldeep Yadav, Jasprit Bumrah, Mohammed Shami, Mohammed Siraj
England: Jonny Bairstow, Dawid Malan, Joe Root, Ben Stokes, Jos Buttler (capt/wkt), Liam Livingstone, Moeen Ali, Chris Woakes, David Willey, Adil Rashid, Mark Wood
Umpires: Adrian Holdstock (RSA), Rod Tucker (AUS)
TV Umpire: Ahsan Raza (PAK)
Match Referee: Richie Richardson (WIS)