Anthony Joshua's world title fight has "extra precautions" to ease fears about finding a late replacement for Kubrat Pulev, says promoter Eddie Hearn.
Britain's unified heavyweight champion is due to defend his world titles against Pulev on December 12, live on Sky Sports Box Office, in Joshua's first fight on home soil for over two years.
Dillian Whyte's rematch with Alexander Povetkin was recently postponed after the Russian tested positive for Covid-19, while new opponents have been regularly drafted in during the pandemic, but Hearn hopes to avoid such issues with Joshua-Pulev.
Asked about a standby opponent, Hearn told Sky Sports: "No, Kubrat Pulev will be making his way to London shortly, sooner than we think, and he will be entering the bubble weeks in advance.
"A lot of these top heavyweights and these guys who are earning considerable purses are being constantly tested on a daily basis.
"You look at Derek Chisora, I think he was getting tested every other day. We will bring Pulev here. Every international fighter has to be tested before they travel, and we will make sure he's in the bubble, in an enclosed environment, because you just can't risk it.
"Normally on fight week, you get a five or 10 per cent chance that a fight could fall through. Here it's 50-50, for every fight.
"When you talk about a fight of that size, you have to take extra precautions and that will be making sure both guys are in a bubble, nice and early, and are locked away under strict surveillance to make sure that they're good to go for fight night."
Could a late replacement for Pulev be found?
American Charles Martin, who previously defended and lost the IBF title against Joshua, is the next available IBF challenger after rising back to No 2 in the governing body's rankings.
But Martin's manager Mike Borao says his fighter would have no 'obligation' to step in at late notice to fight Joshua.
"No, Charles is not on standby, but he is the next highest available contender," Borao told Sky Sports.
"Therefore, if the fight is cancelled for any reason, a number of scenarios could present. If Joshua is injured, I think it is very possible Martin and Pulev could fight for the vacant IBF title. In that case, IBF rule procedures would be followed.
"If Pulev is injured, although Charles is the next available contender, I doubt Joshua would opt for that bout, likely resulting in a vacated title as well.
"In either case, if Joshua versus Pulev fails to take place for any reason, I think Charles will have a very good chance of fighting for his old title.
"Charles does not have an obligation to be ready for December 12. Charles enjoys rights pursuant to IBF rules.
"The Pulev negotiations seemed a bit laboured due to Pulev's mandatory status. I don't think Joshua would entertain negotiations with Charles knowing massive bouts against Tyson Fury are looming."
What is the testing process for Pulev?
Hearn has confirmed that Pulev will undergo a series of Covid-19 tests, along with any other overseas fighter on the Joshua bill.
He said: "With the international fighters they test them several times, so they test them on arrival. They test before they fly. Negative? Yes! Then they land, and they test again. Negative? Yes!
"Then they test them again on the Wednesday. It's like three heart attacks, all over the space of five days. That's how it's going to be."