Neither side picked up a point in September, so a head-to-head scrap for survival may commence when they meet at Helsinki's Olympic Stadium.
Match preview
There is already a six-point gap between the top two and the bottom two in Group 3, as England and Greece lead the way after both won twice last month, leaving Finland and the Republic of Ireland with a big task to avoid either direct demotion or a relegation playoff.
The Finns entered another season under the management of long-serving head coach Markku Kanerva, who led his nation to Euro 2020 and has since kept them afloat in the Nations League's second tier.
However, the Nordic nation suffered a major setback at the start of their third straight League B campaign, losing 3-0 in Greece while producing just one shot on target.
That was followed by a 2-0 defeat to England at Wembley Stadium, which left Kanerva's side propping up the four-team standings.
Each of Finland's last five away games has seen them ship at least two goals, so they will surely breathe a sigh of relief to be back on home soil, where a weekend clash with England follows Ireland's visit.
After failing to win any of their first five meetings with Thursday's opponents, the Finns have since won back-to-back games against their Irish counterparts - both by a 1-0 scoreline in the 2020-21 Nations League.
With two home defeats already, relegation must be a serious concern for the Republic of Ireland, who are only above Finland in the table by virtue of a slightly less lousy goal difference.
After losing to England in Dublin - with goals from former 'Boys in Green' Declan Rice and Jack Grealish rubbing salt into the wound - they went on to concede twice in the second half of a 2-0 reverse against Greece.
Now, new boss Heimir Hallgrimsson stands in distinct danger of becoming the first Ireland manager to lose each of their first three competitive games in charge.
His first camp brought no points, no goals and very few chances, as the Republic dropped closer to an all-time low in the FIFA world rankings: over the past four years, they have slid from 34th down to 62nd, with 70th spot being their worst-ever placing.
Under Hallgrimsson, interim coach John O'Shea and former manager Stephen Kenny, Ireland have suffered 10 defeats in their last 15 matches, with only three ending in victory - two of which came against Gibraltar.
After three straight third-place finishes in League B groups, the Boys in Green are therefore in danger of finally falling through the trapdoor, unless they can start a revival by taking points off Finland.
That may be easier said than done, as Ireland have failed to even score in 12 of their 18 Nations League matches to date, while going winless through all eight away games.
Finland Nations League form:
L
L
Finland form (all competitions):
L
W
L
D
L
L
Republic of Ireland Nations League form:
L
L
Republic of Ireland form (all competitions):
D
L
W
L
L
L
Team News
Heimir Hallgrimsson has made a number of changes to his Republic of Ireland squad for this month's gathering, with Matt Doherty, Alan Browne, Callum Robinson and Jake O'Brien all missing out.
Will Smallbone and captain Seamus Coleman are both injured, so Festy Ebosele of Watford could start at right-back in the latter's absence.
Uncapped pair Jack Taylor and Mark McGuinness are promoted from the Under-21s, while Mikey Johnston, Jamie McGrath and Finn Azaz have all been recalled. Stoke City striker Tom Cannon - who scored four times in one game last week - has been put on standby.
After scoring his first Champions League goal in September, Adam Idah will compete with Evan Ferguson, Troy Parrott and Sammie Szmodics for selection up front.
Meanwhile, Finland have recently moved away from their classic 4-4-2 formation, switching to a flexible box midfield and putting more emphasis on attacking via their full-backs.
Adam Stahl and Manchester City teenager Tomas Galvez filled those wide roles against Greece, but Jere Uronen was selected in England.
Bayer Leverkusen goalkeeper Lukas Hradecky captains the home side, while Rennes midfielder Glen Kamara usually links up with all-time top scorer Teemu Pukki in the final third. The latter, now 34, is thriving in MLS with Minnesota United, but Venezia captain Joel Pohjanpalo offers an alternative option.
Fredrik Jensen could play a part too, having scored the only goal in both wins over Ireland four years ago - each of his last three international strikes have come in Helsinki.
Finland possible starting lineup:
Hradecky; Stahl, Hoskonen, Ivanov, Galvez; Peltola, Schuller; Jensen, Kamara, Antman; Pukki
Republic of Ireland possible starting lineup:
Kelleher; Ebosele, Collins, O'Shea, Brady; Molumby, Cullen, Knight; Ogbene, Idah, Szmodics
We say: Finland 1-1 Republic of Ireland
While they tend to struggle on the road, Finland have won both of their last two home matches and are now faced by an Irish side bereft of confidence - but the Boys in Green do boast some attacking talent.