Captain Joe Root was hit in the abdomen while warming up for day four of the second Ashes Test Sunday and missed the start of play in another blow to England's struggling team.

The visitors are desperately trying to save the clash in Adelaide after being skittled in the first innings for 236 in reply to Australia's 473 for nine.

Australia captain Steve Smith opted not to enforce the follow on and his team resumed on 45 for one, looking to build an unassailable lead.

But Root, the world's premier Test batsman, was not on the field.

"Joe Root will not be on the field at the start of play today after being hit in the abdomen during throwdowns in the warm-up before play," an England team spokesman said.

"He is currently being assessed by the England medical team."

Root scored 62 in the first innings before he and Dawid Malan (80) were out, sparking a batting collapse that saw them slump from 150 for two to 236 all out.

Day four got under way in the midst of another Covid-19 scare after a member of the media tested positive to the virus.

"In accordance with our pre-planning we are undertaking a deep clean of the relevant areas and are facilitating alternative facilities for relevant officials as required," Adelaide Oval said in a statement.

It comes just days after Australian captain Pat Cummins was ruled out of the Test after being deemed a close contact of a coronavirus case.

He was initially ordered to isolate for seven days on his hotel room but was later allowed to return home to Sydney on a private charter flight.