West Brom boss Slaven Bilic says a number of his squad tested positive for coronavirus in the international break.
Bilic lost Branislav Ivanovic and Matheus Pereira for the defeat by Tottenham on 8 November after they supplied positive test results in the build-up to the game.
Striker Callum Robinson also tested positive after going on international duty with the Republic of Ireland.
All three are clear to face Manchester United at Old Trafford on Saturday.
However, Bilic says he is still waiting on other members of his squad and has moved his side's training schedule to allow time for the results to come in.
"We had a few players positive but I can't say the names," the Croatian said. "We are doing everything we can. We are waiting for results."
Bilic also said he had been part of a Premier League manager's meeting on Wednesday that spent a long time discussing whether to return to five substitutes.
He said he was mindful of player welfare and decisions should be made with that in mind but feels the Premier League should make the decision.
He said: "It would benefit every club in sense of player welfare given the schedule, especially for clubs in Europe. It is hard and difficult.
"We spoke about it yesterday for two or three hours. The break wasn't long enough and welfare is the most important thing. The Premier League has to decide."
Bilic also believes that urgent action is needed regarding dementia.
The Professional Footballers' Association (PFA) is setting up a new taskforce to further examine the issue of brain injury diseases in the game.
The union will be in contact with Dawn Astle, the daughter of former West Brom favourite Jeff Astle, who died aged 59 in 2002.
Neuropathologist Dr Willie Stewart said the former England forward died of a brain condition normally linked to boxers, and that it was caused by heading footballs.
"It is very important," Bilic said of the new taskforce. "We are connected with Jeff Astle. His family has done a brilliant job with the foundation (the Jeff Astle Foundation
founded in 2015 dedicated to raising awareness of brain injuries in all sports).
"The PFA has to do something, how I don't know. The players need to be properly looked after. This is even more important than a few more substitutes."