McCrystal, the WBO concessionaire in New Zealand says the fight would be staged under the WBO flag.
Welliver and Jankelson are currently in the US, preparing for his next fight.
However, the boxing scene in Auckland is confused about Tua's future intentions..
His lawyer, Blair Edwards said: "There aren't really any developments [for a next fight for Tua]. There are a few ideas hovering around but nothing concrete. I know David has been using the 'R' word [retirement] a few times lately but I haven't heard anything directly on that either." Others in the fight game have also heard that Tua - who is understood to be in Samoa and did not return calls - is contemplating retirement again. Edwards said the kerfuffle over Tua's demand that the result of the last fight against Barrett be overturned because the American tested positive for a banned substance was not a reason for any delay in signing on for the next fight with Barrett - "but it didn't help".
McCrystal said the WBO agreed with his assessment that Barrett's win should stand because of the lateness of the drugs test and the questionable procedure. Edwards said: "No one has really having any firm discussions on that [the next fight with Barrett] and David Tua has not signed up to any fight."
He also said he had not heard from Welliver's camp about a possible fight "but I don't know if they have been talking to David directly yet".
If Tua is tempted by Welliver's offer of a $500,000 purse, it could be a testing fight.
Welliver has had 62 fights - a lot for a 28-year-old whose first pro fight was as an 18-year-old - for a total record of won 52, drawn five and lost five. However, Welliver has said he felt his career really did not start until 2008 when he fought and lost to US-resident, Cuban Odlanier Solis on a technical knock out.
Solis went on to fight Vitali Klitschko - but hurt a knee and was graphically knocked out in round one of their clash, damaging his reputation.
Solis is a better fighter than that and has been re-building his own career and Welliver, currently in the USA, says he realised that day against Solis that he was competitive.
"I consider my career to really have started after the Solis fight. That is when I realised I could fight," he said in an earlier interview.
In the three years since, he has been busy - fighting 17 times, unbeaten, including successfully defending his WBC Continental Americas heavyweight title.
Last week, in Auckland, he knocked out Moyoyo Mensah, of Ghana, to retain his WBO Asia-Pacific title, the WBC Asian heavyweight title, the interim WBO Oriental heavyweight title and the New Zealand national title.
Welliver, originally from Spokane, Washington but now fighting out of New Zealand, still boxes in the US and has a big following in China, of all places, as he has twice defended his WBC Continental title there.
Previous WBC Continental champions include Chris Arreola, Michael Moorer, James Toney, Lamon Brewster, Barrett, Evander Holyfield and Leon Spinks - nearly all of whom went on to be or were former heavyweight champions or got title shots.
Welliver's increased standing in world boxing and the possibility of a fat purse might be tempting for Tua - but that word 'retirement' continues to raise questions.
