Kobayashi has joined Celtic ahead of the January window on a five-year deal and will be part of the squad on the first day of the new year.
The former Japan youth international played more than 40 times for Vissel Kobe in the 2022 Japanese season, missing only two games in the league.
Postecoglou is delighted to have the defender join his team as he thinks there is a dearth of left-sided centre-backs and Kobayashi thankfully fits the bill.
Celtic bought the likes of Reo Hatate and Daizen Maeda, both from the Japanese league, last January and Postecoglou thinks it is good to bring in players in the winter window as it gives them time to adjust.
Speaking to Celtic’s official site, Postecoglou said: “We’re really pleased.
“Yuki is someone that we’ve been following for a while and it was a great opportunity to bring him in.
“He’s a left-sided centre-back, and they’re hard to find.
“I think we saw last year that bringing in guys nice and early gives us the opportunity to bed them in, in that six-month period of the second half of the season, and we’re really looking forward to having him as part of the group.”
Celtic brought in only one new centre-back in the summer, but with the addition of Kobayashi they have added to that department.