THE CROWD capacity for Sunday's Western Derby will remain at 75 per cent, but Western Australia Premier Mark McGowan has warned that could be reviewed on Sunday morning after a hotel security guard tested positive to COVID-19.

The AFL remains prepared for a crowd of up to 45,000 for the clash between West Coast and Fremantle after restrictions were eased in WA after the State's recent snap three-day lockdown.

A new positive case has been uncovered, however, in a security guard working at a quarantine hotel, with two of his housemates also testing positive. The man had been in the community during his potentially infectious period.

"At this time, football is going ahead with the 75 per cent crowd … if that changes, we'll let people know as soon as we can," Mr McGowan said on Saturday. 

The Premier warned, however, that although a lockdown was not being enforced for the Perth and Peel communities, that could change as early as Sunday morning if needed.

"We’re effectively in a holding pattern and I hope we can avoid going back into lockdown," Mr McGowan said.

The Perth and Peel communities must return to wearing masks inside and outside from 6pm AWST Saturday but were urged to start doing so immediately. 

Fans were already required to wear masks when attending Sunday's Derby as part of increasing the capacity to 75 per cent.

The government announced the increased capacity for the highly anticipated Derby on Thursday after Fremantle hosted North Melbourne last Saturday night at an empty Optus Stadium during the recent lockdown.