The England squad, including captain Ben Stokes, were hit with a virus on the eve of the first Test against Pakistan in Rawalpindi.
About 14 members of the traveling group of players and coaches were asked to rest at the hotel on Wednesday.
About half of the 16-man squad were affected, with just five attending an optional training session.
The first match of the three-test series begins on Thursday (05:00 GMT).
Lancashire all-rounder Liam Livingstone is set to make his Test debut for England, while fly-half Ben Duckett has been recalled to play his first Test in six years.
Joe Root, Zak Crawley, Harry Brook, Ollie Pope and Keaton Jennings were the players in practice Wednesday, while head coach Brendon McCullum also attended.
The symptoms of those affected are unrelated to Covid-19 and the hope is that there will be a recovery within 24 hours.
England did not appoint an official vice-captain during Stokes’ reign as skipper, although Pope captained the team in Stokes’ absence in a warm-up game against the England Lions last week.
The test will be England’s first in Pakistan in 17 years after their tour of the country was halted following an attack by gunmen on the Sri Lanka team bus in 2009.
England returned for the first time for a T20 series in September and November, winning 4-3.
