Melbourne radio talkback host Derryn Hinch is battling another mystery illness and does not know when he will be back on air.

Hinch was admitted to Cabrini hospital in suburban Malvern, on Wednesday.

He has undergone tests, including MRIs, X-rays and a CAT scan that revealed he had suffered blood poisoning.

But the radio drive time show host said he did not know what caused it.

“I can’t tell you because they (doctors) haven’t told me,” Hinch told News Limited.

He said he does not know when he will be back on air.

It is the second health major scare for Hinch in 12 months.