| Okan Derıcı | Galatasaray (TUR) |  Turkey | Forward |
| O'Kane, Eunan | Bournemouth (ENG) / Northern Ireland U21 / Republic of Ireland U21 |  Republic of Ireland | |
| Okay Yokuşlu | Kayserispor (TUR) / Turkey U19 | Turkey | Midfield |
| Okazaki, Shinji | Stuttgart (GER) |  Japan | Midfield |
| Okine, Priscilla | Spartak Subotica (SRB) |  Ghana | Defender |
| Okore, Jores | Nordsjælland (DEN) / Denmark U21 / Denmark |  Denmark | Defender |
| Okoronkwo, Isaak | Rostov (RUS) |  Nigeria | Defender |
| Okotie, Rubin | Sturm (AUT) |  Austria | Forward |
| Okoyino Da Mbabi, Célia | Bad Neuenahr (GER) / Germany WOCO |  Germany | Forward |
| Okriashvili, Tornike | Illychivets (UKR) / Georgia / Georgia U21 |  Georgia | Midfield |
| Oksanen, Jaakko | Finland U17 |  Finland | Forward |
| Okulewicz, Anna | Poland WU17 |  Poland | Goalkeeper |
| Olabarrieta, Amaia | Athletic (ESP) / Spain WOCO |  Spain | Midfield |
| Olabe, Roberto | Spain U17 | Spain | Midfield |
| Óladóttir, Gudmunda | Iceland WU19 / Iceland WOCO |  Iceland | Forward |
| Ólafsdóttir, Laufey | Valur (ISL) / Iceland WOCO | Iceland | Midfield |
| Olafsdóttir, Doris | Klaksvík (FRO) / Faroe Islands WOCO |  Faroe Islands | Defender |
| Olafsdóttir, Alda | Iceland WU17 | Iceland | Forward |
| Ólafsson, Árni | ÍA (ISL) / Iceland U21 | Iceland | Goalkeeper |
| Olah, Adrian | Turnu Severin (ROU) |  Romania | Midfield |
| Olăr, Corina | Olimpia Cluj (ROU) / Romania WOCO | Romania | Defender |
| Olawale Ojuola, Noah | Midtjylland (DEN) | Nigeria | Defender |
| Olberdam | Marítimo (POR) |  Brazil | Midfield |
| Olcan Adın | Trabzonspor (TUR) | Turkey | Midfield |
| O'leary, Ryan | Kilmarnock (SCO) | Republic of Ireland | Defender |
| Oleksy, Paweł | Piast (POL) / Poland U21 | Poland | Defender |
| Olesen, Allan | Åtvidaberg (SWE) | Denmark | Defender |
| Olesen, Casper | Denmark U17 | Denmark | Forward |
| Olić, Ivica | Wolfsburg (GER) / Croatia |  Croatia | Forward |
| Oliech, Dennis | Ajaccio (FRA) |  Kenya | Forward |
| Oliinyk, Iaroslav | Ukraine U21 |  Ukraine | Defender |
| Olijve, Frank | Zwolle (NED) |  Netherlands | Midfield |
| Olimpa, Kevin | Bordeaux (FRA) |  France | Goalkeeper |
| Öling, Ria | PK-35 (FIN) / Finland WU19 | Finland | Forward |
| Oliseh, Isaac | Midtjylland (DEN) | Nigeria | Midfield |
| Oliva, Oriol | Andorra U21 |  Andorra | Goalkeeper |
| Oliva, Petr | Chrudim (CZE) / Czech Republic FUT |  Czech Republic | Defender |
| Oliynyk, Denys | Dnipro (UKR) | Ukraine | Midfield |
| Olkowski, Paweł | Górnik (POL) / Poland U21 | Poland | Defender |
| Olsen, Súni | Faroe Islands | Faroe Islands | Midfield |
| Olsen, Malene | Brøndby (DEN) / Denmark WOCO | Denmark | Defender |
| Olsen, Danny | Midtjylland (DEN) | Denmark | Midfield |
| Olsen, Anna | Brøndby (DEN) | Denmark | Goalkeeper |
| Olsen, Klæmint | Faroe Islands U21 / Faroe Islands | Faroe Islands | Forward |
| Olsen, Adelheid | Klaksvík (FRO) | Faroe Islands | Defender |
| Olsen, Teitur | Faroe Islands U19 | Faroe Islands | Defender |
| Olsen, Patrick | Internazionale (ITA) / Denmark U19 | Denmark | Midfield |
| Olsen, Dania | Faroe Islands WU19 | Faroe Islands | Forward |
| Olsen, Meinhard | Faroe Islands U17 | Faroe Islands | Forward |
| Olsen, Robin | Malmö (SWE) | Denmark | Goalkeeper |
