| Martin O'Neill | IRN | 2001/02 | 2 | 1 | 0 | 1 | 6 | 6 | Celtic Glasgow, Aston Villa | | |
| Michael O'Neill | IRN | 2010/11 | 2 | 2 | 0 | 0 | 3 | 0 | Shamrock Rovers | | |
| Ernst Ocwirk | AUT | 1962/63 | 8 | 5 | 1 | 2 | 12 | 4 | Sampdoria, Köln | | |
| Giancarlo Oddi | ITA | 1993/94 | 0 | 0 | 0 | 0 | 0 | 0 | Lazio | | |
| Francesco Oddo | ITA | 1984/85 | 4 | 2 | 1 | 1 | 10 | 5 | Lazio, Reggiana, Salernitana, Venezia, Messina, Giulianova | | |
| Massimo Oddo | ITA | 2016/17 | 2 | 2 | 0 | 0 | 5 | 0 | Pescara, Udinese | | |
| Oddone | ITA | 1923/24 | 2 | 2 | 0 | 0 | 4 | 1 | Derthona | | |
| Takeshi Okada | GIA | 2004/05 | 0 | 0 | 0 | 0 | 0 | 0 | Yokohama F·Marinos | | |
| Aldo Olivieri | ITA | 1950/51 | 7 | 3 | 1 | 3 | 13 | 11 | Inter, Udinese, Triestina | |  |
| Nino Ollio | ITA | 2011/12 | 0 | 0 | 0 | 0 | 0 | 0 | Rappresentativa Val di Susa | | |
| Cosmin Olăroiu | ROM | 2005/06 | 0 | 0 | 0 | 0 | 0 | 0 | Politehnica Timișoara | | |
| Hans Ooft | OLA | 1992/93 | 0 | 0 | 0 | 0 | 0 | 0 | Japan | | |
| Ferdi Oppenheim | AUT | 1922/23 | 2 | 0 | 2 | 0 | 2 | 2 | Milan | | |
| Nevio Orlandi | ITA | 2008/09 | 2 | 1 | 1 | 0 | 6 | 2 | Reggina | | |
| Corrado Orrico | ITA | 1979/80 | 4 | 2 | 1 | 1 | 6 | 4 | Udinese, Inter, Empoli | | |
| Fernando Orsi | ITA | 2007/08 | 1 | 1 | 0 | 0 | 5 | 1 | Livorno | | |
| György Orth | UNG | 1935/36 | 2 | 1 | 1 | 0 | 5 | 1 | Genoa | | |
| Ivica Osim | BOS | 1992/93 | 2 | 1 | 1 | 0 | 1 | 0 | Panathinaikos Athens | | |
| Stojan Osojnak | CRO | 1965/66 | 0 | 0 | 0 | 0 | 0 | 0 | Rijeka | | |
| Giuseppe Ottina | ITA | 1955/56 | 1 | 0 | 1 | 0 | 2 | 2 | Novara | | |
| Valeriano Ottino | ITA | 1968/69 | 0 | 0 | 0 | 0 | 0 | 0 | Biellese | | |
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