Bairstow was initially in the selection, but the England and Wales Cricket Board later said he had been kicked out of the rest of the summer and the T20 World Cup after sustaining a lower limb injury in a freak accident while playing golf at Leeds on Friday.
Bairstow said in an Instagram post that he injured himself after slipping on the golf course and would have to undergo surgery.
Roy was an integral part of England’s white ball team and his explosive stick atop the order embodied the team’s aggressive approach as they won their first 50-time World Cup title in 2019.
The 32-year-old has struggled for points this summer and managed 76 points overall in his last six Twenty20 Internationals, which made his position untenable for the World Cup and the previous seven-game Twenty20 series in Pakistan.
In-form tailors Chris Woakes and Mark Wood, who both last played for England on the West Indies Test tour in March, have recovered from their respective injuries to feature in both squads.
The England squad includes Chris Jordan (finger) and Liam Livingstone (ankle) who will skip the Pakistan tour to continue their rehabilitation, the ECB announced on Friday.
Captain Jos Buttler, who is recovering from a calf injury, will tour Pakistan but will only be available to play in the latter stages of the series.
“In Buttler’s absence, Moeen Ali will be the team captain,” the ECB said.
Jordan Cox, Tom Helm, Will Jacks, Olly Stone and Luke Wood are the five unselected players named in England’s squad for the Pakistan series which kicks off on September 20 in Karachi.
Former world champions England begin their Twenty20 World Cup campaign against Afghanistan on October 22 in Perth.
T20 World Cup team: Jos Buttler (captain), Moeen Ali, Harry Brook, Sam CurranChris Jordan, Liam Livingstone, Dawid Malan, Adil Rashid, Phil Salt, Ben Stokes, Reece Topley, David Willey, Chris Woakes, Mark Wood
Reservations: Liam Dawson, Richard Gleeson, Tymal Mills
Pakistan Tour Team: Jos Buttler (captain), Moeen Ali, Harry Brook, Jordan Cox, Sam Curran, Ben Duckett, Liam Dawson, Richard Gleeson, Tom Helm, Will Jacks, Dawid Malan, Adil Rashid, Phil Salt, Olly Stone, Reece Topley, David Willey , Chris Woakes, Luke Wood, Mark Wood.