"Shuntaro Koga". fckariya.jp (in Japanese). Retrieved 16 December 2022.
"古賀俊太郎選手 加入のお知らせ" [Announcement of Shuntaro Koga joining]. fckariya.jp (in Japanese). 16 January 2021. Retrieved 16 December 2022.
hochi.news
"１９歳・古賀、ベルギー２部サン・ジロワと契約" [19-year-old Koga signs contract with Belgian second division Saint Gilloise]. hochi.news (in Japanese). 7 February 2018. Retrieved 16 December 2022.
"古賀 俊太郎 選手加入のお知らせ" [Announcement of Shuntaro Koga player participation]. renofa.com (in Japanese). 10 February 2020. Retrieved 16 December 2022.
soccerway.com
int.soccerway.com
Shuntaro Koga at Soccerway. Retrieved 27 November 2020.
targma.jp
www2.targma.jp
"海外からの練習生 古賀俊太郎について、小倉勉SDは「キャンプに参加することで見極めたい」" [Regarding trainee Shuntaro Koga from overseas, SD Tsutomu Ogura said, "I want to find out by participating in the camp."]. targma.jp (in Japanese). 18 January 2019. Retrieved 16 December 2022.
Nakata, Toru (15 April 2018). "ベルギー2部で奮闘する19歳・古賀俊太郎 15歳で単身渡欧、前例のない道筋でプロに" [19-year-old Shuntaro Koga struggles in the Belgian second division At the age of 15, he travels to Europe alone and becomes a professional on an unprecedented path]. sports.yahoo.co.jp (in Japanese). Retrieved 16 December 2022.
yscc1986.net
"古賀 俊太郎選手加入のお知らせ" [Announcement of Shuntaro Koga joining]. yscc1986.net (in Japanese). 15 July 2022. Retrieved 16 December 2022.
