And on Wednesday, a psychiatrist also said his mental capacity was sound.
After his consultation, he was pushed in his wheelchair through botanic gardens in Basel for dinner with his family.
Prof Goodall will give a final media conference on Wednesday with Dr Nitschke and Life Circle lawyer Moritz Gall, before on Thursday taking his final journey from his hotel to a facility 20 minutes drive away.
In an earlier interview with The Associated Press, Prof Goodall spoke of his determination to end his life, saying he started seriously thinking about it after his quality of life deteriorated over the past year.
He does not have a terminal illness but cited a lack of mobility and doctor's restrictions, and is taking advantage of Switzerland's assisted-suicide laws because it is prohibited back home in Western Australia, where his daughter, son and grandchildren live.
Prof Goodall, who does not believe in the afterlife and has been a member of Exit International for 20 years, said he tried clumsily to take own his life at least three times - and then finally decided to get professional help.
He has been looking to draw attention to his story in the hope countries like Australia change their laws to be more accepting of assisted suicide.
Prof Goodall said after reaching middle age, people should be allowed to decide themselves whether to use medicine to take their own lives.
"I wouldn't suggest that it's available to everyone, and just going and buying it off the shelf," he said.
"I think there are plenty of people who might misuse that.
"But I would accept that it should be done by doctors' prescription - but they should be free to prescribe."
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.
Suicide Call Back Service 1300 659 467.