Yokoyama, who scored four times at Jordan 2018, including the only goal in her side's win over Australia in the final, returns to the national team having missed last month's 3-1 win over New Zealand.
While head coach Asako Takakura's 23-strong travelling party consists largely of the same players who helped Japan to a second-successive continental championship, they will travel without veterans Kumagai and Sakaguchi.
Takakura explained the absence of the duo, who have made a combined 206 senior international appearances.
"Most of the other players are usual faces, but we excluded Saki Kumagai due to scheudle conflicts with her club and Mizuho Sakaguchi due to injury," she revealed.
"I am looking forward to seeing who steps up in that leader role, as we are lacking our core players."
Despite the absence of two of her most trusted and experienced leaders, Takakura has reason to approach the tournament - which also features Australia, Brazil and hosts United States - with confidence.
Since a 6-2 defeat to the Netherlands in February, Japan have lost just once in 10 outings, and their head coach believes they are primed to improve on their performances at the 2017 edition of the tournament, which saw them finish without a win.
"Last year, we failed to play our game and came back empty handed, so we would like to show the world just how much we have improved since," Takakura said.
"This is a restart ahead of next year’s World Cup and we will continue to look for new talents and build up on what we have worked on thus far."
The squad also includes 21-year-old defender Aimi Kunitake, who earned a maiden senior international call-up by virtue of strong league performances for Nojima Stella Kanagawa.
Japan's Tournament of Nations campaign begins with a clash against the world champion United States side on July 26, before they face Brazil and Asian rivals Australia over the course of the following week.
Japan squad - 2018 Tournament of Nations
Number Player Name Club
1 IKEDA Sakiko Urawa Red Diamonds Ladies
2 UTSUGI Rumi Seattle Reign FC (USA)
3 SAMESHIMA AYA INAC Kobe Leonessa
4 MIYAKE Shiori INAC Kobe Leonessa
5 ICHISE Nana Mynavi Vegalta Sendai Ladies
6 ARIYOSHI Saori Nippon TV Beleza
7 NAKAJIMA Emi INAC Kobe Leonessa
8 IWABUCHI Mana INAC Kobe Leonessa
9 KAWASUMI Nahomi Seattle Reign FC (USA)
10 TANAKA Mina Nippon TV Beleza
11 NAOMOTO Hikaru SC Freiburg (GER)
12 SUGASAWA Yuika Urawa Red Diamonds Ladies
13 HASEGAWA Yui Nippon TV Beleza
14 SAKAGUCHI Moeno Albirex Niigata Ladies
15 SUMIDA Rin Nippon TV Beleza
16 MOMIKI Yuka Nippon TV Beleza
17 YAMASHITA Ayaka Nippon TV Beleza
18 MASUYA Rika INAC Kobe Leonessa
19 YOKOYAMA Kumi AC Nagano Parceiro Ladies
20 HIRAO Chika Albirex Niigata Ladies
21 SHIMIZU Risa Nippon TV Beleza
22 KUNITAKE Aimi Nojima Stella Knagawa
23 MIURA Narumi Nippon TV Beleza
Source: the-afc.com