Construction to begin this year on state-of-the-art Thumbay Veterinary Hospital At Thumbay Medicity
Sarri previously coached Higuain at Napoli when he scored a Serie A record 36 goals in a league campaign in 2015/16.
That sort of goalscoring prowess is what Chelsea have been badly missing in recent months, with Sarri's lack of confidence in Alvaro Morata and Olivier Giroud forcing Eden Hazard into an unfamiliar centre-forward role.
"They're a few hours into signing a contract today," Sarri said.
Chelsea play Tottenham in Thursday's League Cup semifinal second leg at Stamford Bridge, bidding to overturn a 1-0 deficit to reach the February 24 final.
The Blues had until 1200 GMT to register Higuain for the match, but Sarri says "it's impossible" for the Argentina international to feature.
Higuain has been on loan at AC Milan from Juventus this season, scoring just once in his past 12 appearances for the Rossoneri.
"We hope he'll bring goals, he'll start scoring for us," Sarri said.
"It's very difficult in January to find one of the most important strikers in the world. So I think the club is working very well because it's not easy to get a new striker."
Sarri criticised his players following last Saturday's Premier League loss to Arsenal, saying his group of players were difficult to motivate.
Asked about the response from his players this week, he said: "I think we need to react on the pitch. The rest is nothing.
"We discussed with the players how to try to improve the approach, the motivation, the determination, so we are trying to change something in training, in pre-match, in everything. I think we all have to react on the pitch, of course."
Construction to begin this year on state-of-the-art Thumbay Veterinary Hospital At Thumbay Medicity
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