West Ham assistant Alan Irvine believes testing labs are "stretched to the limit" amid delays over Premier League clubs receiving back their results.
The Hammers host Wolves on Sunday but will be without manager David Moyes as well as players Issa Diop and Josh Cullen, who all tested positive for coronavirus on Tuesday.
News of those results only came through an hour before the club's Carabao Cup tie with Hull and this weekend's opponents could find themselves in a similar situation.
Wolves boss Nuno Espirito Santo revealed they were only tested on Friday prior to Sunday's away fixture and insisted: "Faster results of the test would help all the teams immensely."
On the lateness in getting back their results, Irvine said: "That was a shock to us.
"Normally the test results have come back very quickly. I think the labs are now finding it a bit more difficult because of the amount of tests they are having to do for people outside of football.
"They are being stretched to the limit. The tests we did on Wednesday took a long time to come back as well, so it is a situation that is out of our control.
"It was a terrible time to find out. We found out 20 past six before a game that was kicking off at half-seven that the manager and a couple of players had to go, but full credit to the players and staff who immediately kicked into game mode."
With Moyes self-isolating, Irvine will be the lead figure on the touchline at the London Stadium on Saturday, but the former Everton boss will manage remotely.
How the 57-year-old will do that has not been figured out yet as West Ham look to get off the mark after back-to-back league defeats to Newcastle and Arsenal this season.
"We will look at the best way of working so he is in touch with us during the game," Irvine revealed.
"He watched the (Hull) game the other night but everything happened too late for us to set anything up.
"I usually sit up in the stand anyway to get a better view and I am in contact with the bench. I would imagine it will be a reversal of that.
"David will be able to be in contact with the bench and any information he wants to get onto the pitch he can pass on."
West Ham's neighbours Leyton Orient also had an outbreak of Covid-19 cases this week and it resulted in their cup tie with Tottenham being called off, with the Premier League side eventually handed a bye.
Spurs paid for the Os' squad to be tested and while the Hammers offered to pay for Hull's tests, it was turned down.
"It was obviously ironic it was our own tests that proved to be the problem," Irvine admitted.
"There could well have been a few players in their squad who, like our players and David, were showing no symptoms at all, feeling perfectly well and were actually carrying the virus.
"I think all the Football League clubs would probably like regular testing but of course it comes down to cost – and who is going to fund that?"
