England's Ashes campaign has once again been rocked by Covid-19, this time leaving its batters in a particularly frustrating bind.

The English side was training at the SCG ahead of the start of Wednesday's fourth Test in Sydney but it was disrupted when a net bowler was alerted of a positive test during the session.

It left England without net bowlers as all the bowlers were deemed close contacts.

Cricbuzz's Bharat Sundaresan reported one of the batters saying the drama was a "shambles".

England has been hit hard by Covid, having four positive cases among its group — although no players — during the Boxing Day Test.

That outbreak led directly to head coach Chris Silverwood returning a positive test on Sunday, meaning he will miss the Sydney Test.

Three of Silverwood's five family members have now tested positive to Covid and there are nine positive cases within the England camp.

It's unclear what role Silverwood will have in the lead up to the SCG Test as England's sole selector, but it is hoped he will be able to return to the team's set-up for the fifth Test in Hobart starting on January 14.

He is joined on the sidelines by spin coach and former Black Cap Jeetan Patel, fast bowling coach Jon Lewis, strength and conditioning coach Darren Veness and ring in coach Adam Hollioake, all who have test positive or, in Hollioake's case, been deemed a close contact.

It forced English skipper Joe Root to take over some of the coaching duties at the SCG.

Despite the drama, opening batter Zak Crawley said he was happy for the game to go ahead.

"I 100 per cent want to play this Test so definitely comfortable," he told reporters.

Australia has been relatively unaffected, losing Travis Head to a positive case but having all other players, staff and family members cleared.

Australia's Covid numbers have skyrocketed in recent days and the Big Bash has been effected with positive cases in several of the teams.

It has led to calls for the remainder of the tournament to be played in a Victorian hub.