This is a highly unusual shirt in that it bears the sponsors - Bord Gais instead of the sponsor you would normally expect to see - Opel. It has the number 18 on the reverse. This shirt was almost certainly a League of Ireland XI player's shirt - Bord Gais sponsored the League of Ireland during the mid-1990s. Shirts with the Bord Gais sponsorship logo were never made available to the general public for sale.
The shirt is definitely a players shirt because no long-sleeved replica shirts were ever produced. Also, the Umbro logo has been embroidered into the shirt's fabric - on replica shirts it would have been printed on instead. Unfortunately, I have no idea which match this shirt was worn in or which player wore it but it is a rare shirt nonetheless.