Mbokazi and his agent, Basia Michaels, arrived in the Windy City on Friday for talks with the club, who are offering Mbokazi a lengthy deal and Pirates a healthy transfer fee.
It would be a massive windfall for the club, who bought Mbokazi through their junior ranks.
A move away from South Africa for the 20-year-old centre-back has been the subject of much speculation over the last months, especially with South Africa national team coach Hugo Broos suggesting he leave sooner rather than later if he is to realise his potential.
Left-footed Mbokazi made his debut in March and has come on leaps and bounds in a short period of time, and was handed the captain’s armband at Pirates this season, including their MTN8 success.
He also made a South Africa debut in June and has since won five caps, the latest in last weekend’s 3-1 friendly win over Zambia in Gqeberha.
If he signs for Chicago Fire, he will likely have played his last game for Pirates, even if the new MLS season does not start until February.
They will not want him to feature in the Carling Knockout final, where Pirates face Marumo Gallants in Polokwane on December 6 and are searching for their second trophy of the season.
It would leave him short of match practice before the Africa Cup of Nations finals in Morocco, although after December 6, there are no other games scheduled for South African clubs before the Cup of Nations kicks off on December 21.
Bafana players must report to camp 14 days before the tournament kicks off on December 7.
Chicago Fire have been interested in Mbokazi for several months, tracking his playing progress but also investigating his personality.