Coronavirus dominated the English League Cup schedule on Tuesday as West Ham played despite their coach and two players having tested positive, while Tottenham Hotspur's game was called off.
West Ham said manager David Moyes and players Issa Diop and Josh Cullen only found out their test results after they had arrived at the London Stadium for their game against Hull City.
Diop and Cullen had been named in the starting line-up.
"The manager and both players immediately left the stadium and have returned home," the Hammers said in a statement.
"All three, who are asymptomatic, will now follow Public Health England and Premier League guidelines and protocols."
Assistant coach Alan Irvine took charge of West Ham in Moyes' absence with the Premier League side hammering their lower-tier opponents 5-1.
Robert Snodgrass scored the opening goal before Sebastien Haller and Andriy Yarmolenko scored two each.
The Premier League coronavirus protocols state Moyes, Diop and Cullen will have to isolate for 10 days.
That would mean they miss the Premier League game against Wolverhampton Wanderers on Sunday.
Tottenham's match was called off two hours before kick-off because Leyton Orient players contracted COVID-19.
"Discussions are ongoing between the relevant stakeholders in regards to the implications of the fixture not taking place," the English Football League, which organises the competition, said in a statement.
It was not clear whether Tottenham had been awarded victory by default or whether the match would be rescheduled.
Manchester United got their first win of the season by beating second-division Luton Town 3-0 in goalkeeper Dean Henderson's competitive debut for the Red Devils.
Juan Mata gave United the lead from the penalty spot on halftime before substitutes Marcus Rashford and Mason Greenwood added goals late on.
Henderson, 23, impressed last season on loan at Sheffield United and will challenge David de Gea as United's No.1.
West Bromwich Albion lost 5-4 on penalties to second-tier Brentford after the game ended 2-2, with goalkeeper David Raya making the deciding save in the shootout.
League Two side Newport County produced a surprise result to beat Watford 3-1.