Roy did not partake in the cricket action after he appeared to suffer from a hamstring tear while fielding in England's eight-wicket win over the West Indies on Friday, which was later confirmed upon MRI scans.
Meanwhile, England skipper Eoin Morgan was also subject to a back spasm during the same match and his condition will be assessed in the next 24 hours to determine whether he will play against Afghanistan.
"England batsman Jason Roy, who left the field during West Indies' innings in the ICC Cricket World Cup fixture on Friday due to left hamstring tightness, underwent an MRI scan on Saturday in London," an ECB spokesperson said.
"The MRI confirmed that Roy has suffered a hamstring tear.
"He is set to miss England's next two matches in the ICC Cricket World Cup against Afghanistan (18 June) and Sri Lanka (21 June)."
Discussing Morgan's injury woe, the team spokesman added: "The spasm has settled down and will be monitored over the next 24 hours ahead of England's next match against Afghanistan tomorrow (Tuesday) at Old Trafford, Manchester."
Morgan insisted he would recover in time before the Old Trafford clash as he was part of an indoor net session at Lancashire's headquarters ground.
"It's drastically improved," he said of his back. "I've had a hit in the nets and I'm aiming to play tomorrow.
"I've had extra treatment and medication in the last two days which has helped me no end.
"I had a small hit in the nets and hopefully I'm fit to play," the 32-year-old added.
"If the game was today I think I could play. It all depends on how I pull up in the morning."
Roy has been scoring consistently for England this tournament as he struck a fifty in a winning cause against South Africa in the World Cup opener and brought up the highest individual score of the tournament versus Bangladesh in their domineering 153-run victory.
His only flop came in England's shock defeat to Pakistan by a narrow margin of 14 runs at Trent Bridge.
England Test captain Joe Root was decided as a makeshift opener alongside the regular Jonny Bairstow during England's innings against the West Indies as he took the honours with a magnificent century in his new role.
Morgan, however, said Roy would be replaced by specialist opener James Vince, who is yet to make his debut World Cup appearance.
Morgan felt Roy's injury was not too serious as he would soon be making a comeback to the team to be part of the playing XI in the latter stages of the tournament.
"I certainly believe Jason will play again in this tournament," he said.
"At the moment he's going to be assessed continuously over the course of the next week.
"He's out of the next two games. So we'll see how he pulls up after that.
"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."