Newcastle United boss Steve Bruce says some of the club's coronavirus victims are battling extreme exhaustion as they attempt to fight their way back to fitness.
The Magpies will once again be without a number of unnamed players for Saturday's home match against Fulham as a result of the lingering effects of the Covid-19 outbreak, which prompted the club to close their training ground at the end of last month.
Defender Federico Fernandez and midfielder Isaac Hayden have returned to the fold in the past week but some of their team-mates have not been so fortunate.
"We've had the full range," said Bruce. "We've had vomiting, sores, mouth ulcers, no smell, no taste -- but the big thing, of course, and which is the worrying thing, is the welfare of one or two or three of them.
"It's not great at all. We're still going to be weeks and that long-term Covid is something which you wouldn't think possible in young, fit, athletes. Unfortunately, it is so."
The Newcastle boss said the most worrying element was lingering fatigue.
"They go for a walk for half an hour and then they want to go back to bed," he said. "It's as brutal as that. It has been very difficult. It has been a really difficult couple of weeks."
Two members of Bruce's squad have been hit particularly hard by the virus, and the 59-year-old admits their plight shows the gravity of the situation.
He said: "My thoughts are with the two players, and the welfare of them. It's frightening when you think they are young and fit and absolutely supreme athletes.
"If anybody needs reminding of how serious this is, then we have witnessed it."