Waqar Younis believes Pakistan will need an "A-plus" performance if they are to beat arch-rivals India in a high-stakes World Cup match on Sunday.
Pakistan's 41-run defeat by champions Australia at Taunton on Wednesday has left them eighth in the 10-team table.
Although they still have more than half of their group games still to play, Sarfaraz Ahmed's side cannot afford many more slip-ups if they are to finish among the top four that will qualify for the semi-finals.
"When Pakistan play India it's always a huge game, but their meeting on Sunday is shaping up to be more crucial than ever," Pakistan fast-bowling great Waqar wrote in a column for the International Cricket Council.
"If Pakistan want to stay in the tournament, they have to bring an A-plus performance and win that game."
"The match has always meant so much to both countries. There will be billions watching the game."
History will be against Pakistan at Old Trafford, with India having won all six previous meetings between the subcontinental cricket giants at the World Cup.
India are also in fine form, with Virat Kohli's side having beaten both South Africa and Australia in their two previous group games before Thursday's no result against New Zealand.
"Pakistan's track record is very mixed, but that's all gone," said Waqar. "That's all history. It's a new game, a new day."
But Waqar said Pakistan could take heart from the last major one-day international tournament in England and Wales, when they lost to India in their opening match of the 2017 Champions Trophy only to bounce back in style to thrash them by 180 runs in the final.
Left-arm quick Mohammed Amir returned career-best figures of 5-30 against Australia on Wednesday as the defending champions were dismissed for 307.
Waqar, who formed a superb new ball-partnership with left-arm pace great Wasim Akram, said Pakistan needed to do more to back up Amir.
"Mohammad Amir didn't get any support from the other end (against Australia).No one really saw the comeback coming and for that, you have to take your hat off to Amir. Full marks to him for the way he bowled.
"Even with the new ball, I thought he bowled quite nicely. He could have picked up more than five wickets in the end. He was unfortunate with a couple of nicks early on.
"Amir bowled superbly. He showed us all his cutters, variations and short-pitched deliveries."
The gifted Amir's career looked finished when he was given a five-year ban and jail sentence for his role in a spot-fixing scam during the 2010 Lord's Test against England.
"I think we all know Amir is mentally very, very strong," said Waqar. "He showed once again that class is permanent -- he is, no doubt, a match-winner."
