Koulibaly is set for a £34million switch to Stamford Bridge after eight seasons at Serie A side Napoli.
The Senegalese star is set to join his new teammates in the United states when he successfully passes his medical.
He will pen a five-year deal with the Blues and becomes the club's second summer signing after Raheem Sterling completed his switch from Manchester City earlier this week.
Juventus were firmly in the running to sign the 31-year-old but Napoli made it clear that their wish was not to sell their star defender to an Italian club and Chelsea took full advantage.
As a result, Juve are now believed to be switching their focus to Arsenal defender Gabriel who is 'open' to the move, The Independent claim.
The report says the Turin-based club have already made contact with the Gunners regarding the availability of the 24-year-old.
Arsenal are believed to have put a £40m price tag on the Brazilian who has impressed since his arrival from French side Lille in 2020.
Gabriel has three years left on his contract and boss Mikel Arteta will not want to lose a key component of his backline.
He made 39 appearances last season across all competitions, scoring five times and helping Arsenal to a much improved fifth-placed league finish and qualification for the Europa League.
Meanwhile, Chelsea are plotting a defensive refurbishment this summer and Koulibaly looks to be the first one through the door with the club also eyeing a move for Paris Saint-Germain centre-back Presnel Kimpembe.
The Blues are light in defence following the departures of free agents Antonio Rudiger and Andreas Christensen and while Rudiger's exit in particular, was a bitter pill to swallow, the impending arrival of Koulibaly will more than make up for it.