Bulgaria were promoted to League B owing to their second-placed finish in Group C3 in 2018-19, while Ireland finished rock bottom of B4 but avoided relegation due to the format change.
The 2018-19 UEFA Nations League truly was a tale of two halves for the Bulgarian national team, who enjoyed three wins from their first three but then failed to triumph in their remaining fixtures.
However, the nine points that Georgi Dermendzhiev's players picked up against Slovenia, Norway and Cyprus was enough to see them take second spot and secure a route into League B for the 2020-21 tournament.
Notwithstanding the controversy surrounding racist abuse directed towards England players in the European Qualifiers, Bulgaria endured a torrid qualification run and only managed to win one of their eight games in Group A - a 1-0 triumph over the Czech Republic back in November.
Nevertheless, Dermendzhiev's side still have the chance to qualify for next year's tournament through the playoffs, where they must overcome either Iceland or Romania should they defeat Hungary in the semi-finals of Path A.
Given their woeful run of form in all competitions - with only one win to show from their last 14 including friendlies - avoiding an immediate relegation back down to Group C would constitute a successful Nations League campaign for Bulgaria.
Dermendzhiev's men last took to the pitch in February for a friendly against Belarus, where they ultimately succumbed to a 1-0 defeat.
Ireland would have initially been relegated to League C for the 2020-21 Nations League, but with 16 teams now occupying the four groups instead of 12, Ireland's spot in League B is safe for now.
Under McCarthy, the Boys in Green failed to win any of their four matches in the 2018-19 edition - drawing twice to Denmark and losing both matches with Wales.
Since then, Ireland managed to enjoy a decent run in their Euros qualification group - only losing one of their eight games - but as is the case with Bulgaria, Kenny's men have been forced to settle for a spot in the playoffs.
Ireland and Bulgaria last locked horns in a friendly back in September, and it was the Boys in Green who took the spoils in a 3-1 victory, with Alan Browne, Kevin Long and James Collins on the scoresheet.
Bulgaria form (all competitions): LDLLWL
Ireland form (all competitions): DWDLWD
Goalkeeper Plamen Iliev played in all three of Bulgaria's victories in the 2018-19 Nations League, but the Ludogorets shot-stopper has undergone surgery on an Achilles injury and is not in the squad.
As for Ireland, Troy Parrott - currently on loan at Millwall from Tottenham Hotspur - suffered a muscular injury in a friendly victory over Southend United and has been forced to withdraw.
Kenny is sweating over the fitness of James McCarthy, who is struggling with a calf problem, but the midfielder is reportedly training well ahead of Thursday's clash.
Bulgaria possible starting lineup:
Georgiev; Cicinho, Zanev, Dimitrov, Nedyalkov; K. Malinov, Kostadinov; Nedelev, Iliev, Ivanov; Isa
Ireland possible starting lineup:
Randolph; Doherty, Egan, Duffy, Stevens; Hourihane, McCarthy; Robinson, Hendrick, McClean; Connolly
We say: Bulgaria 0-2 Ireland
Kenny will be determined to get off to a flying start as he gears up for his inaugural match as Ireland manager, and the Boys in Green are preparing for a clash with a Bulgaria side who have struggled for form in recent times, so we are backing Kenny's men to get the job done in convincing fashion on Thursday evening.