| Olsen, Dánjal Rói | Faroe Islands U21 |  Faroe Islands | Forward |
| Olsen, Áka Klein | Klaksvík (FRO) | Faroe Islands | Midfield |
| Olsen, Hervør | Faroe Islands WU17 | Faroe Islands | Midfield |
| Olsen, Jensa | Faroe Islands WU17 | Faroe Islands | Forward |
| Olsen, Tóra | Faroe Islands WU17 | Faroe Islands | Midfield |
| Olsen, Mathias | Denmark FUT |  Denmark | Midfield |
| Olshevski, Aleksandr | Mapid Minsk (BLR) / Belarus FUT |  Belarus | Defender |
| Olsson, Jonas | West Brom (ENG) / Sweden |  Sweden | Defender |
| Olsson, Martin | Blackburn (ENG) / Sweden | Sweden | Defender |
| Olteanu, Calin | Târgu Mureş (ROU) |  Romania | Forward |
| Olthof, Nienke | Netherlands WU19 |  Netherlands | Goalkeeper |
| Olthuis, Nadja | Netherlands WOCO | Netherlands | Goalkeeper |
| Oluwafemi, Ajilore | Groningen (NED) |  Nigeria | Midfield |
| Omar Ramos | Valladolid (ESP) |  Spain | Midfield |
| Omarov, Bauyrzhan | Akzhayik (KAZ) / Kazakhstan U21 |  Kazakhstan | Defender |
| Ómarsdóttir, Katrín | KR (ISL) / Iceland WOCO |  Iceland | Midfield |
| Ómarsson, Orri Sigurdur | Iceland U19 | Iceland | Midfield |
| Omazić, Filip | Bosnia and Herzegovina U17 |  Bosnia and Herzegovina | Defender |
| Omeirat, Mohammed | Ibra Göteborg (SWE) / Sweden FUT | Sweden | Forward |
| Ömer Erdoğan | Bursaspor (TUR) |  Turkey | Defender |
| Ömer Kahveci | Bucaspor (TUR) / Turkey U21 | Turkey | Goalkeeper |
| Ömer Şişmanoğlu | Antalyaspor (TUR) | Turkey | Forward |
| Ömer Toprak | Leverkusen (GER) / Turkey | Turkey | Defender |
| Omeradžić, Zerina | Bosnia and Herzegovina WOCO | Bosnia and Herzegovina | Defender |
| Omerbegović, Bahrudin | Orlić (BIH) / Bosnia and Herzegovina FUT | Bosnia and Herzegovina | Goalkeeper |
| Omeruo, Kenneth | Den Haag (NED) | Nigeria | Defender |
| Omilade, Navina | Wolfsburg (GER) |  Germany | Midfield |
| Omirou, Savvas | Omonia (CYP) / Cyprus FUT |  Cyprus | Forward |
| Omrani, Billel | Marseille (FRA) |  France | Forward |
| Onazi, Ogenyi | Lazio (ITA) | Nigeria | Midfield |
| Onciu, Marius | Ceahlăul (ROU) | Romania | |
| Ondrušová, Lucia | Slovan Bratislava (SVK) / Slovakia WOCO |  Slovakia | Midfield |
| O'Neil, Gary | West Ham (ENG) |  England | Midfield |
| Ongenda, Hervin | PSG (FRA) | France | Forward |
| Onica, Alexandru | Moldova |  Moldova | Midfield |
| Onicaş, Mihai | Viitorul (ROU) | Romania | Midfield |
| Onofraş, Marius | Iaşi (ROU) | Romania | Forward |
| Onuoha, Nedum | QPR (ENG) | England | Defender |
| Onur Kıvrak | Trabzonspor (TUR) / Turkey | Turkey | Goalkeeper |
| Onwuachi, Benjamin | Xanthi (GRE) | Nigeria | Forward |
| Onyewu, Oguchi | Málaga (ESP) |  USA | Defender |
| Onzia, Lenie | Arsenal (ENG) / Belgium WOCO |  Belgium | Midfield |
| Opanasenko, Yevhen | Metalurh Zaporizhya (UKR) / Ukraine U21 |  Ukraine | Midfield |
| Oparanozie, Desire | Rossiyanka (RUS) | Nigeria | Forward |
| Opare, Daniel | Standard Liège (BEL) |  Ghana | Defender |
| Oper, Andres | Nea Salamis (CYP) / Estonia |  Estonia | Forward |
| Oprea, Olivia | Olimpia Cluj (ROU) / Romania WOCO | Romania | Defender |
| Oprita, Daniel | Mordovia (RUS) | Romania | Forward |
| Or, Hasidim | Israel U17 |  Israel | Forward |
| Orachev, Miki | Bulgaria U17 |  Bulgaria | Midfield |
