| Club: | FC Seoul |
| Season: | 2021 |
| Manager: | Park Jin-sub (–6 September) An Ik-soo (6 September–) |
| Chairman: | Huh Tae-soo |
| Stadium: | Seoul World Cup Stadium |
| League: | K League 1 |
| Cup1: | Korean FA Cup |
| Chrtitle: | Chairman |
| Lowest Attendance: | 0 |
| Prevseason: | 2020 |
| Nextseason: | 2022 |
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The 2021 season is FC Seoul's 38th season in the K League 1.
| Type | Date | Opponents | Result | Score | Scorers | Notes | |
|---|---|---|---|---|---|---|---|
| Practice matches during winter training spell in Changwon, South Korea | 25 January 2021 |  KC University | 2–0[4] | Ki Sung-yueng, Go Yo-han | |||
| 27 January 2021 | Soongsil University | 7–1[5] | 3 quarters match | ||||
| Practice matches during winter training spell in Jeju, South Korea | 31 January 2021 | Korea University | 7–0[6] | Na Sang-ho, Go Yo-han (2), Park Jung-bin Kwon Sung-yun, Lee In-gyu (2) | 3 quarters match | ||
| 7 February 2021 | Gyeongju Korea Hydro & Nuclear Power FC | 2–0[7] | Na Sang-ho, Go Yo-han | 3 quarters match | |||
| 10 February 2021 | Dong-Eui University | 1–0[8] | Park Chu-young | ||||
| 11 February 2021 | Dankook University | 3–0[9] | |||||
| 13 February 2021 | Kyung Hee University | 6–0[10] | Cho Young-wook,  Aleksandar Paločević (2), Kang Sung-jin Park Jung-bin, Lee In-gyu | 3 quarters match |
See main article: 2021 K League 1.
See main article: 2021 Korean FA Cup.
Fixtures and Results at FC Seoul Official Website
| Position | Name | Notes |
|---|---|---|
| Manager | Park Jin-sub | |
| Assistant Manager | Yoo Kyoung-youl | |
| First Team Coach | Park Hyuk-soon | |
| Lee Jung-youl | ||
| Reserve Team Coach | Kim Jin-kyu | |
| Cho Sung-yong | ||
| Goalkeeping Coach | Choi Hyun | |
| Fitness Coach | Hwang Ji-hwan | |
| U-18 Team Manager | Cha Du-ri | |
| U-18 Team Coach | Yoon Hyun-pil | |
| U-18 Team Goalkeeping Coach | Bang Hyung-gon | |
| U-18 Team Fitness Coach | Jung Hoon-gi | |
| U-15 Team Manager | Kim Young-jin | |
| U-15 Team Coach | Kim Byung-chae | |
| Yoon Si-ho | ||
| U-15 Team Goalkeeping Coach | Yoon Hyun-wook | |
| U-15 Team Performance Coach | So Ki-dong | |
| U-12 Team Manager | Kim Byung-chae | |
| U-12 Team Coach | Seo Ki-man | |
| U-12 Team Coach | Lee Ji-hun | |
| Scout | Lee Won-jun | |
| Jung Jae-yoon | ||
| Position | Name | Notes |
|---|---|---|
| Manager | An Ik-soo | |
| Assistant Manager | Vacant | |
| First Team Coach | Park Hyuk-soon | |
| Lee Jung-youl | ||
| Reserve Team Coach | Kim Jin-kyu | |
| Cho Sung-yong | ||
| Goalkeeping Coach | Choi Hyun | |
| Fitness Coach | Hwang Ji-hwan | |
| U-18 Team Manager | Cha Du-ri | |
| U-18 Team Coach | Yoon Hyun-pil | |
| U-18 Team Goalkeeping Coach | Bang Hyung-gon | |
| U-18 Team Fitness Coach | Jung Hoon-gi | |
| U-15 Team Manager | Kim Young-jin | |
| U-15 Team Coach | Kim Byung-chae | |
| Yoon Si-ho | ||
| U-15 Team Goalkeeping Coach | Yoon Hyun-wook | |
| U-15 Team Performance Coach | So Ki-dong | |
| U-12 Team Manager | Kim Byung-chae | |
| U-12 Team Coach | Seo Ki-man | |
| U-12 Team Coach | Lee Ji-hun | |
| Scout | Lee Won-jun | |
| Jung Jae-yoon | ||
| Yoo Kyoung-youl |
| No. | Pos. | Nationality | Player | Notes |
|---|---|---|---|---|
| South Korea | Yu Sang-hun | |||
| South Korea | Hwang Hyun-soo | |||
| South Korea | Cho Seok-young | |||
| Spain | Osmar | |||
| South Korea | Kim Jin-sung | |||
| South Korea | ||||
| South Korea | Ki Sung-yueng (captain) | |||
| Uzbekistan | Ikromjon Alibaev | Out | ||
| South Korea | Ji Dong-won | |||
| South Korea | ||||
| South Korea | Cho Young-wook | |||
| South Korea | ||||
| South Korea | Kwon Sung-yun | |||
| South Korea | Out | |||
| South Korea | ||||
| South Korea | Han Chan-hee | Conscripted | ||
| Australia | Connor Chapman | |||
| South Korea | Kim Jin-ya | |||
| South Korea | ||||
| South Korea | Jung Han-min | |||
| South Korea | Lee In-gyu | |||
| South Korea | Yang Han-been | |||
| South Korea | ||||
| South Korea | Yoon Jong-gyu | |||
| South Korea | Conscripted | |||
| South Korea | Discharged | |||
| Serbia | ||||
| South Korea | Ko Kwang-min | |||
| South Korea | Kang Sang-hee | |||
| South Korea | Baek Jong-bum | |||
| South Korea | Jeong Jin-wook | Out | ||
| South Korea | Yang Yu-min | |||
| South Korea | ||||
| South Korea | Kim Ju-sung | Conscripted | ||
| South Korea | Son Ho-jun | |||
| South Korea | Kim Won-gun | |||
| South Korea | ||||
| South Korea | Discharged | |||
| South Korea | ||||
| South Korea | Cha Oh-yeon | |||
| South Korea | Kang Seong-jin | |||
| South Korea | ||||
| South Korea | ||||
| Brazil | ||||
| No. | Pos. | Nationality | Player | Moving To | Loan Period | |
|---|---|---|---|---|---|---|
| South Korea | Lee Hak-seon | Pocheon Citizen | February 2020–December 2021 | |||
| South Korea | Jung Won-jin | Gimcheon Sangmu | May 2020–November 2021 | |||
| South Korea | Park Dong-jin | Gimcheon Sangmu | May 2020–November 2021 | |||
| South Korea | Kim Woo-hong | FC Namdong | July 2020–September 2022 | |||
| South Korea | Lee Seung-jae | Chungnam Asan FC | February 2021–December 2021 | |||
| South Korea | Oh Min-gyu | Yangpyeong FC | February 2021–December 2021 | |||
| South Korea | Kim Ju-sung | Gimcheon Sangmu | March 2021–May 2022 | |||
| South Korea | Jung Hyun-cheol | Gimcheon Sangmu | March 2021–September 2022 | |||
| South Korea | Han Chan-hee | Gimcheon Sangmu | June 2021–December 2022 | |||
| South Korea | Jeong Jin-wook | Gimhae FC | July 2021–December 2021 |
Note: Where a player has not declared an international allegiance, nation is determined by place of birth.
※ In: Transferred from other teams in the middle of the season.
※ Out: Transferred to other teams in the middle of the season.
※ Discharged: Transferred from Gimcheon Sangmuu for military service in the middle of the season (registered in 2021 season).
※ Conscripted: Transferred to Gimcheon Sangmu for military service after the end of the season.