If Roy misses out, Hampshire captain James Vince could be in line for his first ODI appearance in nearly two years, although Monday saw England call up Kent's Sam Billings as additional batting cover for the series finale in Leeds.
Roy sustained a laceration to the little finger of his right hand while fielding during England's 86-run victory over India at Lord's on Saturday and a team spokesman said Monday: "He remains a doubt for tomorrow (Tuesday) and will have a fitness test in the morning at the ground to ascertain whether he’ll be fit to play."
Vince last played a one-day match for England during the tour of Bangladesh in October 2016.
Opener Alex Hales has missed the whole of the series with India with a side strain while Dawid Malan, his replacement, has already been released to take part in the second-string England Lions' four-day match with India A.
Vince lost his Test place at the start of the season in one of the first major decisions by new England selection chief Ed Smith.
But he has been in brilliant domestic white-ball form, scoring more than 500 runs during Hampshire's victorious One-Day Cup campaign.
England may be top of the world ODI rankings but, following last year's Champions Trophy semi-final loss to Pakistan, doubts remain about their ability to win truly high-stakes games.
Beaten into the dirt
Now Durham quick Mark Wood hopes England, who will aim to win a maiden World Cup title when they stage the 2019 edition, will respond well to the pressure if Tuesday's winner-takes-all contest and lay down a marker head of next year.
"I think this has an impact for the World Cup," Wood told reporters at Headingley on Monday. "We can use it as a game where it might be (like) a semi-final or a knockout game.
"It's a series decider here, which will be like a World Cup match -- it's a must-win," the England paceman added.
"Luckily, over the past year we've managed these situations really well. Hopefully we can carry on that trend."
India, second to England in the ODI standings, won the series opener by a decisive eight wickets at Trent Bridge only to be equally well-beaten at Lord's.
"It's two very good sides -- when they're on top, they really are on top, you keep your foot on the throat and don't let opposition up," said Wood.
"Everyone in the England team will hold their hands up and say in the first game we were absolutely drilled, we were beaten into the dirt. We knew we had to improve for the second game.
"I don't know why the margins are so big, maybe it's just two really good teams and when they are on top the quality really comes through," he added. "I'd like to think that this one could still be a big margin for us."