After just one season at Milan, Bonucci will return to his old club, having struggled to show his best form at San Siro.
30-year-old Higuain has become the fall guy for Juve following Cristiano Ronaldo's recent move to Turin and has been deemed as surplus to requirements in Turin.
However, weeks of negotiations could come to nothing because of AC Milan's imminent signing of Caldara.
Marotta met with Milan representatives on Wednesday afternoon to discuss the move, and emerged to respond to reporters who asked if a deal had been struck, according to La Gazzetta dello Sport. Higuain will move for 18m euros on loan with an option to buy for another 36m.More news: Man United man tells Jose Mourinho he wants to leave this summer
Juventus are reluctant to let him leave so the Evening Standard claims Chelsea have now tabled a £35.5m bid for team-mate Caldara after holding formal talks with sporting director Fabio Paratici over the weekend. Sarri wants to bring Higuain to replace Morata in front of the goal. Higuain has played under the Chelsea manager at Napoli in 2015-16, where he scored record 36 goals in Serie A.
The Juve star's brother and agent, Nicolas, was at Casa Milan earlier this week to meet with their new GM Leonardo. The key meeting to arrange the deal happened on Tuesday.
AC Milan seem to have got the advantage by offering Leonardo Bonucci back to Juventus in a swap deal whilst Mattia Caldara from Juventus, will also join Milan as Bonucci's direct replacement. But they will have to submit the bid quickly as EPL's transfer window closes a week before Serie A.