Lithuania, on the other hand, have nothing to play for in the group, sitting bottom on one point with just this final fixture to complete.
Portugal blew their chances of finishing top of the group when they lost 2-1 to Ukraine in their last game, handing their opponents an unassailable eight-point gap on the chasing pack.
It was the first loss of Portugal's qualifying campaign but it was a significant one, allowing Serbia to move within a point of them and keep the pressure on heading into the final round of fixtures.
However, with second-bottom Luxembourg to follow after Lithuania, Cristiano Ronaldo and co. will feel confident of picking up maximum points from their final two games and assuring themselves of a spot at Euro 2020.
Ronaldo himself hit four in a 5-1 win the last time these two sides met, and has scored half of his nation's 14 qualifying goals so far in this campaign.
Lithuania, whose sole point in the group came at home in a 1-1 draw against a similarly struggling Luxembourg side, will not relish the prospect of facing the Juventus forward for a second time - and in Portugal.
The Group B minnows have shipped a whopping 19 goals in just seven games, scoring only five in that period.
Lithuania were not even able to take advantage of the Nations League pathway by failing to win their group, instead finishing bottom, losing each of their six games in the competition and suffering relegation to League D.
Instead, Serbia took advantage and they, as well as Ukraine and Portugal, would be guaranteed a playoff place were they to finish outside the two automatic qualification spots.
Portugal form: WWWWWL
Lithuania form: DLLLLL
Portugal boss Fernando Santos was unable to call up a number of players for this round of international qualifying games.
Everton midfielder Andre Gomes suffered a horror ankle injury and is now a long-term absentee, with his return a long way off at present.
All five players were in the last squad, with Guedes, Mario and Semedo all starting in the defeat to Ukraine.
Portugal possible starting lineup:
Patricio; Pereira, Dias, Fonte, Guerreiro; Neves, Moutinho; Fernandes, B. Silva; Ronaldo, A. Silva
Lithuania possible starting lineup:
Setkus; Mikoliunas, Girdvainis, Klimavicius, Andriuskevicius; Kuklys, Simkus; Lasickas, Slivka, Novikovas; Cernych
We say: Portugal 4-1 Lithuania
Portugal will be keen to dispatch their opponents with a minimum amount of fuss and should stroll to a comfortable victory by a sizeable margin.