Smith, in an article for a British daily, revealed that de Villiers was looking to walk away from Test cricket last year itself but was persuaded by Cricket South Africa (CSA) officials to stay on while offering a break of one year.
"It's my belief that AB was looking to walk away from Tests last year at some point, but has been encouraged to carry on by CSA," Smith wrote in a column for Britain's Independent newspaper.
"His personal prerogative is ensuring he does all he can to add as much longevity to his international career as possible, as well as taking into account the harsh realities of touring such as the amount of travel involved, and the toll that takes on your body.
"AB is due to assess his future with CSA later this summer, and my advice to him would be to step away from the captaincy, and concentrate his energy in to maintaining his levels in white-ball cricket for the next two years," Smith added.
de Villiers has not played Tests since sustaining an elbow injury in the series against Australia last year.
He was appointed South Africa's Test captain in 2016 after Hashim Amla resigned from the post but he held the post for just an year before resigning in December last year and handed over the reins to Faf Du Plessis.
"Put simply, if that is what's best for him and the longevity of his career, then that is what's best for South African cricket," Smith wrote.
"Those criticising AB, and this decision in particular, need to ask themselves whether they would rather de Villiers played in the upcoming (Test) series and walked away from international cricket in a year, or have the opportunity to see him go on and play for his country at another big ICC tournament."
de Villiers has been heavily criticised in the last six months for 'picking and choosing' the matches that he wants to play with some questioning his commitment to South Africa.
This was because the flamboyant batsman opted to sit out of the England Test series even after he had acquired full fitness.
Ashwell Prince, the former South African cricketer, took a sly dig at de Villiers and CSA after South Africa's humiliating loss to India in the Champions Trophy by saying that it should be the CSA who should decide who will get the honour to represent the country and not the other way around.
"AB has already made huge sacrifices for South African cricket, over such a long period of time, and with the next ICC World Cup just two years away, it's likely that he is targeting that tournament as a swansong to his already illustrious career at the top level."
"What has AB de Villiers got to prove to anyone? He's a star, and those players are often expected to be available all of the time no matter what the consequences might be personally," Smith wrote.
de Villiers has time and again reasserted his ambition to win an ICC Trophy and has repeatedly gone on record to say that he is targeting the 2019 World Cup as his swansong, considering his young family which will see a new addition soon and his burgeoning injuries in recent years.
First Published: June 28, 2017, 11:34 AM IST