"Yeah, it's good luck for us Jason Roy is not playing tomorrow," Naib said. "Roy is one of the best players in the world now in the last two years. He's one of the world-class, best players. "England is a strong side, it's a home side, so everything is going England's side ... (but) we're here to make some good upsets."
England has beaten South Africa, Bangladesh and West Indies but had an upset loss to Pakistan in its second game. Afghanistan has lost to defending champion Australia, Sri Lanka, 2015 finalist New Zealand and South Africa, and not really been close to a win.
But Morgan is wary, because he predicted before the tournament that this Afghan squad would win games. "They haven't managed to do that yet," Morgan said. "So that makes tomorrow, you know, a tougher challenge."
The Old Trafford pitch showed some turn during India's win over Pakistan on Sunday and again is expected to assist the spinners, which helps an Afghan lineup that relies heavily on the slow bowlers and gives England the opportunity to recall Moeen Ali to bolster the batting and provide bowling backup to wrist-spinner Adil Rashid.
Morgan said with Roy out for at least two games with a torn muscle in his left hamstring, James Vince would come into the England lineup as an opener and Joe Root, who scored an unbeaten century when he opened in the eight-wicket win over West Indies last Friday, would revert to No. 3.
Roy limped off after injuring his leg while fielding early in the match against the West Indies. He missed the latter stage of England's ODI series in the Caribbean this year and more time for his county team. Still, Morgan is confident the 28-year-old right-hander will be OK by next week to play Australia.
England is keeping Roy around because of his destructive batting at the top of an innings, his ability to take bowling attacks apart and his integral role in the evolution of the ODI squad since its group-stage exit at the 2015 World Cup. He averages 42 in 80 ODIs and his 180 against Australia in Melbourne last year is England's ODI record. He scored 54 in the tournament opener against South Africa and 153 against Bangladesh in Cardiff.
"He's obviously a huge part of what we've been doing. He's in the best form of his life. So he's very important," Morgan said. "There's a reason we'd keep him around. One, obviously is he's a very key player, but two, is there's a very optimistic chance of him playing."
Afghanistan's game plan isn't a secret, with its bowling attack built around a spin department led by Rashid Khan. Afghanistan had some important wins over Sri Lanka and Pakistan and a draw with India last year at the Asia Cup, and beat West Indies to clinch top spot in the World Cup qualifying tournament.
The step-up to the 10-team World Cup competition has been an experience Naib believes his squad is benefiting from. Conditions on the wickets at Bristol, Cardiff and Taunton haven't been ideal for Afghanistan's spinners so far, but Naib is expecting Old Trafford to be different.
"Rashid is (an) attacking bowler. Every time, he's attacking," Naib said. "Spin is one of the high success rates of the Afghanistan team. If a little bit of spin there, maybe it's a good day for Afghanistan!"
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