He was admitted to Waikato Hospital 11 days ago and expects to be there until at least Wednesday.
"There are lots of things [they are looking at], but there is a kidney complaint," the former test captain said.
"I have had biopsies and God knows what. I had a big scan a couple of days ago and that brought up a few things."
Meads said he had been buoyed by an avalanche of support from family, friends and members of the wider rugby community.
"I would just like to thank everyone for their best wishes and their concern. There have been heaps of phone calls, messages and emails. Everything I have been getting has been marvellous."
The Herald on Sunday revealed Meads' health battle in May.
"I am not too good. I have been crook for a couple of months," he said at the time.
"I am not getting too much better, put it that way."
Meads described his health battle as a "bad patch" but had been told by specialists that he would "come right again".
"All me joints are swelling up, that is the problem. My whole body is swollen," he said.
"It is just a matter of getting on top of it. I am full of drugs and medication. It will come right."
Meads made his All Blacks debut in 1957, aged just 20.
He played his final match for the national team against the British and Irish Lions at Eden Park in 1971, aged 35.
He is now a member of rugby's International Hall of Fame, in 1999 was named the New Zealand Player of the Century and was knighted in 2001.
Meads was the All Blacks manager between 1994-95, as well as serving on the NZRU council and as an All Blacks selector.
