Western United coach John Aloisi has revealed he was left with just four fit players at training earlier this month because of COVID-19.

Alois says about 20 members of his squad have already been struck down by the virus.

Western's most recent game was their 3-1 loss to Melbourne Victory on Boxing Day, but they'll be back in action on Friday when they take on Wellington Phoenix in Wollongong.

Aloisi's squad had a splattering of cases in mid-December.

But the virus quickly became an outbreak within the squad, forcing the league to postpone a series of matches.

All of Western's virus-hit players have now recovered, meaning Aloisi will have a near-full squad to choose from against Phoenix.

It's a far cry from the situation just a few weeks ago.

"Including the full contracted and the scholarship players, 20 players in total (caught COVID-19)," Aloisi said..

"It's a big amount. We ended up getting hit with the majority of players all at the same time.

"The first week against Adelaide we missed a couple of players, and then against Melbourne Victory a few more, and then all of a sudden we had a total of 14 players who couldn't play.

"At one stage we were only training with four players. That doesn't make it easy for you."

Aloisi guesses there are only four or five players who haven't yet caught the virus.

He said those players would need to take extra precautions.

"We're telling them (to be careful) about restaurants and cafes, and going indoors where there's a lot of people or major events," Aloisi said.

"Are they going to get it? Probably. We don't know when or where or how.

"Even when we're travelling we have to ... keep our masks on as much as possible, stay away from crowds as much as possible."

"We test them every day ... but you're only as on top of it as you can be, because you just don't know where it can come from."

Meanwhile, Perth Glory's match against Macarthur FC has been switched to January 26 at Campbelltown Stadium.

The match was originally meant to be played in Perth on January 28, but WA's border closure meant there was no way it could go ahead at HBF Park.