| Osibov, Ivica | MNK Split (CRO) |  Croatia | Forward |
| Osipova, Natalia | Zorkiy (RUS) / Russia WOCO |  Russia | Midfield |
| Osipyan, Olga | Armenia WOCO |  Armenia | Midfield |
| Oskarsson, Anna | Sweden WU17 |  Sweden | Midfield |
| Osman, Leon | Everton (ENG) / England |  England | Midfield |
| Osman, Olexandr | Ukraine U17 |  Ukraine | Defender |
| Osmani, Tefik | Albania |  Albania | Defender |
| Ošomkov, Grigori | Tallinna Kalev (EST) / Estonia FUT |  Estonia | Goalkeeper |
| Ospelt, Philipp | Liechtenstein / Liechtenstein U21 |  Liechtenstein | Forward |
| Ospina, David | Nice (FRA) |  Colombia | Goalkeeper |
| Osredkar, Igor | Litija (SVN) / Slovenia FUT |  Slovenia | Defender |
| Osredkar, Matevž | Litija (SVN) | Slovenia | Defender |
| Ošs, Dāvis | Latvia U19 |  Latvia | Goalkeeper |
| Öst, Jesse | Jaro (FIN) / Finland U21 |  Finland | Goalkeeper |
| Ostapenco, Victoria | Moldova WU19 |  Moldova | Forward |
| Ostapenko, Sergei | Astana (KAZ) / Kazakhstan |  Kazakhstan | Forward |
| Östberg, Mattias | Djurgården (SWE) | Sweden | Defender |
| Østbø, Arild | Start (NOR) / Norway U21 |  Norway | Goalkeeper |
| Östervall, Amanda | Sweden WU17 | Sweden | Forward |
| Östlund, Saija | Finland WU17 | Finland | Defender |
| Ostojić, Miloš | Serbia U17 |  Serbia | Goalkeeper |
| Ostrowska, Karolina | Poland WU17 |  Poland | Defender |
| Ostrowski, Krzysztof | Śląsk (POL) | Poland | Midfield |
| Ostrzolek, Matthias | Augsburg (GER) / Germany U21 |  Germany | Defender |
| O'Sullivan, Fiona | Republic of Ireland WOCO |  Republic of Ireland | Forward |
| O'Sullivan, Denise | Peamount (IRL) / Republic of Ireland WOCO / Republic of Ireland WU19 | Republic of Ireland | Midfield |
| O'Sullivan, John | Republic of Ireland U21 | Republic of Ireland | Forward |
| Osvaldo , Pablo | Roma (ITA) / Italy |  Italy | Forward |
| Osyra, Kornel | Piast (POL) | Poland | Defender |
| Otaki, Ami | Lyon (FRA) |  Japan | Forward |
| Otamendi, Nicolás | Porto (POR) |  Argentina | Defender |
| Otarbayev, Samat | Kazakhstan U21 | Kazakhstan | Goalkeeper |
| Otegen, Gulbaram | Kazakhstan WU19 | Kazakhstan | Goalkeeper |
| Otero, Gabriel | Andorra U17 |  Andorra | Midfield |
| Othon, Quentin | Troyes (FRA) |  France | Midfield |
| Otmani, Mustapha | Municipium (MNE) / France FUT | France | Forward |
| Otrísal, Erik | Slovakia U17 |  Slovakia | Defender |
| Otsu, Yuki | VVV (NED) | Japan | Forward |
| Otte, Jasper | Zulte Waregem (BEL) |  Belgium | Goalkeeper |
| Ottesen, Sölvi | København (DEN) / Iceland |  Iceland | Defender |
| Ottl, Andreas | Augsburg (GER) | Germany | Midfield |
| Ouahabi, Leila | Barcelona (ESP) |  Spain | Defender |
| Oualembo, Christopher | Lechia (POL) |  Congo | Midfield |
| Oubiña, Borja | Celta (ESP) | Spain | Midfield |
| Oudejans, Tessa | Netherlands WOCO |  Netherlands | Forward |
| Oueslati, Abdelkader | Atlético (ESP) |  Tunisia | Forward |
| Ouladboutaher, Faylal | Roubaix (FRA) / France FUT | France | Forward |
| Õunap, Janar | Estonia U19 | Estonia | Defender |
| Õunpuu, Kethy | Estonia WOCO | Estonia | Midfield |
| Ousager, Emil | AGF (DEN) |  Denmark | Goalkeeper |
