It is the second time Mennie has been treated for the issue.

Mennie copped a ball to the head on Monday and underwent tests in hospital but was released that evening.

Mennie has since been sent back to hospital for observation.

"Whilst this is a serious injury, Joe is feeling well. We believe that this is a stable injury and will not require surgery," Cricket Australia chief medical officer Dr John Orchard said.

"As a precautionary measure, Joe has been admitted to hospital for observation and will continue to be assessed by a neurosurgeon to determine best course of action."

Mennie debuted for Australia against South Africa last year.

The Sixers face the Brisbane Heat tonight in their Big Bash League semi-final.