With Derry City having won the domestic treble the previous season, it meant, by virtue of their FAI Cup final appearance, a first taste of European football for City as they gained admission into the European Cup Winners' Cup for the 1989-90 campaign. Despite a warm-up game in the form of a pre-season friendly with Tottenham Hotspur, City found the proposition of Russian side Torpedo Moscow too tough, losing 5-0 away and 1-0 at home.

While performances were not especially poor, City suffered some bad results early on in the season, leaving them in the lower reaches of the table - if not threatened by relegation - by the end of October, at which time they made an incredibly audacious move by signing four Bulgarian international players.
The signings were announced in the matchday programme for the game with Shelbourne on October 29, 1989, accompanied by a picture of them in the shadow of 'The Shed' at Turner's Cross: "Cork City's four Bulgarian internationals, all of whom have in excess of 20 full international caps. [Stefan] Vassilev, an experienced left side of midfield and [Mario] Vulkov a right winger, who scored last week in the the First Division in Sofia. The most experienced, [Sashko] Borissov, is an extremely strong centre-half, and the goalscoring centre forard is [Ilia] Velitchov. Here's hoping they can help improve our recent results and we would like you to give them a warm Cork welcome."

All four were selected for that game, a 1-0 defeat in which Borissov scored an own goal, but it proved to be an ill-fated experiment as all four were gone by the time City hosted Galway on December 10, with Mick Conroy having been given a player/assistant manager role. Despite losing four international players, City's performances actually improved and they began to move up the table, eventually finishing fifth.
On the field, City used the kit worn in the previous season's FAI Cup final, though not featuring the special inscription over the crest and also without the cuffs at the end of the sleeves (left). Midway through the campaign, a long-sleeved version of the shirt was used, while only green shorts and socks were worn for the duration of the season. The change kit was the same as that introduced in 1988, though for 89-90 it was only seen in a short-sleeve configuration, including in the Munster Senior Cup final win over Tramore Athletic (right).