*Club domestic league appearances and goals, correct as of 16:53, 5 July 2023 (UTC) ‡ National team caps and goals, correct as of 21:36, 5 July 2023 (UTC)
Having played football at the Daedong Elementary School in Seoul and the Mokdong Middle School, Kim travelled to Spain as a child, competing in a youth competition, where he attracted the interest of professional side Villarreal.[1] He joined the club in 2015, but was unable to play due to laws in Spain stating that he would be unable to register with the club until he turned eighteen.[1] He spent four years training with Villarreal affiliate CF Cracks, before spending the 2020–21 season with another affiliate, Alboraya UD.[1]
The following season, he was sent to a third affiliate club, Roda, who were competing in the Tercera División RFEF.[2][3] He finished the season with two goals from twenty-five appearances, also playing once in the Preferente Valenciana for Roda's B team.[4] He returned to Villarreal the following season, being assigned to the club's C team in the Tercera Federación.
^ abc"[MD인터뷰]"(이)강인이 형처럼 스페인서 성공할게요!"…비야레알 9년 차 김효기의 '꿈'" [[MD Interview] "I will succeed in Spain like (Lee) Kangin hyung!"... 'Dream' of Kim Hyo-gi, who has been in Villarreal for 9 years]. sports.news.nate.com (in Korean). 4 July 2023. Retrieved 5 July 2023.