Meanwhile, the Slovenians arrive in Frankfurt for their first knockout match at a major tournament, and they will fight for the right to face France or Belgium in the quarter-finals.
Match preview
Despite winning Group F with a game to spare, Portugal's humbling defeat to long-shot outsiders Georgia on Wednesday night saw them fall victim to an historic giant-killing, slightly souring an otherwise impressive performance so far.
Two errors from Benfica centre-back Antonio Silva helped the Georgians score in either half - with Khvicha Kvaratskhelia's stunning opener arriving inside the first two minutes - and a late fightback failed to transpire in Gelsenkirchen.
As back-to-back wins over the Czech Republic and Turkey had already sealed the Selecao's berth in the last 16, head coach Roberto Martinez gladly took the chance to rest a number of players, such as Bruno Fernandes, Ruben Dias, Bernardo Silva and veteran centre-back Pepe.
Nonetheless, a talented squad will surely be stung by just their third loss since exiting the 2022 World Cup to Morocco: defeat also ended a run of 12 straight competitive victories.
Remarkably, Portugal have not lost back-to-back competitive games since Euro 2008; and as only Germany averaged more possession, faced fewer shots and had more goal attempts during the group stage, they will expect to quickly recover.
Martinez and co are still favourites to progress further into what has been dubbed the tougher half of the draw; since lifting the Henri Delaunay trophy in 2016, though, Portugal have lost three of four knockout games at the Euros or World Cup.
Monday's match will bring Slovenia face to face with the Selecao for only the second time, with the first coming as recently as March of this year - a 2-0 friendly victory in Ljubljana.
By contrast with their illustrious opponents, who have played 25 times following the group phase, the Slovenians are now making their debut at the elimination phase of a major tournament, so even getting this far will be reason to celebrate.
Holding out for a drab goalless draw against England in their final Group C game edged Matjaz Kek's side through to the last 16, also extending their unbeaten streak to nine matches.
Having previously drawn with Denmark and then Serbia - who they came within a whisker of beating - a tally of three points placed them third, which was ultimately enough to break new ground for the Slavic nation.
While Slovenia have averaged just 32% possession at Euro 2024 so far - only two teams have ever progressed from the group phase with a lower average share - Kek can call upon a solid squad featuring two genuine stars: captain Jan Oblak and young striker Benjamin Sesko.
Not since a 2-0 loss to Finland 14 games ago had they failed to score before Tuesday's stalemate in Cologne, so the underdogs can certainly pose a threat to one of the favourites for overall victory.
Portugal European Championship form:
W
W
L
Portugal form (all competitions):
W
L
W
W
W
L
Slovenia European Championship form:
D
D
D
Slovenia form (all competitions):
W
W
D
D
D
D
Team News
After heavily rotating his squad last time out, Roberto Martinez will recall a number of key men for Monday's game, with Bernardo Silva, Vitinha and Joao Cancelo among them.
Only Joao Palhinha, goalkeeper Diogo Costa and captain Cristiano Ronaldo were retained against Georgia, and all three should start again in Frankfurt. However, the latter has not scored in any of his last seven major tournament appearances - his longest such drought across the Euros and World Cup - and Goncalo Ramos waits patiently in the wings.
After picking up two yellow cards - both for diving - Rafael Leao will be available again and could start on the Selecao's left wing; Diogo Jota and Francisco Conceicao have both worked their way into contention, though.
Meanwhile, Slovenia will rely on former Primeira Liga star Andraz Sporar and bright hope Benjamin Sesko to lead their forward line once again. The pair have started all three games so far, but are yet to score from a combined 12 shots between them.
Goalkeeper Jan Oblak joined Benfica in 2010 - helping them win the Portuguese treble and reach the Europa League final in his only senior season before leaving for Atletico Madrid - and may expect a busy night against some familiar faces.
Experienced coach Matjaz Kek generally favours a no-nonsense 4-4-2 formation, with Timi Max Elsnik and Adam Gnezda Cerin manning the midfield engine room. His sole change could see Jure Balkovec replace the suspended Erik Janza at left-back.
Portugal possible starting lineup:
Costa; Cancelo, Pepe, Dias, Mendes; Vitinha, Palhinha, Fernandes; B. Silva, Ronaldo, Leao
Slovenia possible starting lineup:
Oblak; Karnicnik, Drkusic, Bijol, Balkovec; Stojanovic, Elsnik, Gnezda Cerin, Mlakar; Sporar, Sesko
We say: Portugal 2-0 Slovenia
Providing Roberto Martinez opts against more experimentation with tactics and personnel, Portugal should have too much firepower for a hardworking Slovenia side to handle.