Shadab Khan, Haider Ali and Haris Rauf are the three players to have tested positive for COVID-19 during the first round of testing ahead of the team's departure for the tour of England.
The three players were asymptomatic until they were tested in Rawalpindi on Sunday, the Pakistan Cricket Board confirmed.
Meanwhile, all-rounder Imad Wasim and left-arm pacer Usman Shinwari, also screened in Rawalpindi, have tested negative and will travel to Lahore on June 24.
All other players part of the 29-man extended squad, barring Shoaib Malik, and the support personnel, excluding bowling coach Waqar Younis and team physiotherapist Cliffe Deacon, underwent tests in Karachi, Lahore and Peshawar on Monday. The results of their tests will be communicated by the PCB tomorrow.
Shadab, the most experienced player of the three, is considered to be a vital cog in Pakistan's white-ball outfit while Haider was set to make his international debut following an impressive string of performances in the domestic circuit. Pace bowling sensation Rauf got his maiden cap in the Bangladesh T20Is in January after a terrific run in the Big Bash League.
The young trio is now uncertain for the England tour with the players required to undergo 14 days of mandatory self-isolation. It remains to be seen whether the PCB would consider replacements as the selectors had earlier named four reserves in Bilal Asif, Imran Butt, Musa Khan and Mohammad Nawaz who serve "as a cover in case any of the players fail pre-tour Covid-19 testing".
Pakistan's preparations for the tour have been beset by challenges posed by the ongoing coronavirus pandemic. The PCB was forced to call off a pre-tour training camp whereas Haris Sohail and Mohammad Amir made themselves unavailable for the series owing to personal reasons.
The touring party will be kept in a "bio-secure" bubble once they reach the United Kingdom where they will have again undergo tests before being allowed to conduct practice sessions.
Pakistan's three-Test series will follow the completion of the red-ball clashes between West Indies and England.