He made his League of Ireland debut on 13 September 1981 for Limerick United before signing for Shamrock Rovers in 1982.
In his time at the City Ground, Gaynor was one of the Forest players who had to cope with the horrors of the Hillsborough disaster during the opening minutes of their FA Cup semi-final against Liverpool.
Despite scoring regularly for the Forest first team he spent the majority of his time as a reserve player, often behind considerably less prolific strikers.
He then returned to his homeland and despite guesting for Shelbourne in a friendly against Tottenham Hotspur he signed for Cork City in August 1993, initially on a months loan.
[6] He had further spells with St Patrick's Athletic, where he scored against Celtic in a friendly,[7] Limerick and Kilkenny City.