Fernando Santos's side, who are the holders of the trophy, thumped Croatia 4-1 on Saturday in their first game of the latest edition, while Sweden suffered a 1-0 home defeat to France.
Sweden can be pleased with their performance against France last time out, with only a Kylian Mbappe effort late in the first period separating the two teams at the end of the 90 minutes.
Janne Andersson's side really need to pick up some points against Portugal, though, if they are to stand a chance of making an impression in Group 3, which is a very tough section on paper.
Sweden actually collected seven points from their four Group B2 games in the 2018-19 UEFA Nations League to finish top of the section, earning promotion to League A for the latest edition.
The Blue and Yellows will mainly be focusing on preparing for next summer's European Championships, though, having finished second in Group F behind Spain to book their spot in the finals.
Portugal, meanwhile, were excellent in their 2020-21 opener on Saturday, thumping Croatia 4-1 in Porto to ensure that they would top the section despite France also picking up a victory on the same night.
A Selecao triumphed in the inaugural season of the UEFA Nations League, beating Switzerland in the semi-finals before recording a 1-0 victory over the Netherlands in the final last June.
Portugal qualified for next summer's Euros courtesy of a second-placed finish in Group B, and they are the defending European champions, having overcome holders France in the 2016 final.
Santos's team will be looking for another three points on Tuesday night ahead of their next two UEFA Nations League matches away to France and at home to Sweden in October.
Sweden Nations League form: LDWWL
Sweden form (all competitions): DWWWWL
Portugal Nations League form: DDWWW
Portugal form (all competitions): WWLWWW
Sweden boss Andersson is expected to stick with the bulk of the XI that started against France on Saturday, with Robin Quaison likely to retain his spot in the final third alongside leading scorer Marcus Berg.
Juventus attacker Dejan Kulusevski appeared off the bench against the world champions to earn just his second cap and could now come into the starting side in a wide position.
As for Portugal, the main talking point surrounds a certain Ronaldo, who missed out against Croatia on Saturday night due to a toe infection. The Juventus forward is expected to return to the XI for this game, though, and will be looking for his 100th goal for the national side.
Everton's Andre Gomes, though, has been forced to withdraw from the squad through injury.
Sweden possible starting lineup:
Olsen; Lustig, Jansson, Lindelof, Bengtsson; Kulusevski, Olsson, Ekdal, Forsberg; Quaison, Berg
Portugal possible starting lineup:
Lopes; Cancelo, Pepe, Dias, Guerreiro; Fernandes, Danilo, Moutinho; Ronaldo, Felix, Bernardo
We say: Sweden 0-2 Portugal
Ronaldo's expected return will be a huge boost for Portugal, who were excellent against Croatia on Saturday night. Sweden's performance against France was impressive, but we are finding it difficult to back against the visitors, ultimately tipping a 2-0 success for the UEFA Nations League holders.