Wolverhampton Wanderers boss Nuno Espirito Santo has said delays in receiving Covid-19 test results were affecting many Premier League clubs as they prepare for matches.
Wolves travel to West Ham United on Sunday and Nuno said at a news conference on Friday that they had still not got the results from tests conducted earlier in the day.
"It's very disruptive for preparation and planning," Nuno told reporters.
"It's tough for us, you get tested - we got tested today - and we don't know the results. We're preparing for the match on Sunday and having the stress about the final result, can you use a player, can you not?
"Faster results of the test would help all teams immensely so we can proceed without having these problems."
West Ham assistant coach Alan Irvine, who took charge for Tuesday's 5-1 League Cup win over Hull City after manager David Moyes tested positive, suggested that the delays could be because of how busy laboratories are.
"Normally test results have come back quickly but the labs are finding it more difficult because of the amount of tests they have to do for people outside football," Irvine added.
"It's a situation that's out of our control. We'll be tested next on Monday and we have the game at Everton (in the League Cup) on Wednesday... we could find ourselves in a situation where we're travelling to Everton not knowing the results."
West Ham, whose players Issa Diop and Josh Cullen are also self-isolating after testing positive, will have Moyes back in charge for Sunday's match although the Scot will be making all the decisions remotely.