West Ham United and Rangers must overturn first-leg deficits Thursday to reach the Europa League final, while Leicester City travels to the Italian capital to face Jose Mourinho's Roma for a place in the Europa Conference League final.
German side Eintracht Frankfurt has the initiative as it prepares to host West Ham after winning 2-1 in the semifinal first leg in London last week with goals from Borussia Dortmund loanee Ansgar Knauff and Japan midfielder Daichi Kamada.
Having knocked out Barcelona in the last eight, it is eyeing a first European final since defeating Borussia Monchengladbach to win the UEFA Cup in 1980.
"This is the most important game of the season for us. We want to get to the final," insisted Swiss midfielder Djibril Sow after Frankfurt lost 2-0 at Bayer Leverkusen on Monday with a much-changed team from the first leg.
Standing in its way is a West Ham side that has knocked out Sevilla and Lyon in the last two rounds and is itself targeting a first European final in 46 years, since it lost to Anderlecht in the Cup Winners' Cup in 1976.
The Hammers have had a fine season but it rather risks ending in anticlimax if they fail to beat Frankfurt given they are now unlikely to finish higher than seventh in the Premier League after a run of one point from four games.
If West Ham does go through it will be the seventh English club to reach the final of the UEFA Cup or Europa League since 2000 and there is still a chance it could be an all-British affair.
Rangers, UEFA Cup runners-up in 2008, welcome RB Leipzig to Ibrox looking to turn around their 1-0 loss in Germany when Angelino's late strike ended the Scottish side's resistance.
Leipzig's push for Champions League qualification via the Bundesliga has stalled after back-to-back defeats, but it would be an enormous achievement for Rangers if they could beat Domenico Tedesco's men.
"Listen, this is now our biggest game of the season," said Rangers defender Borna Barisic after Sunday's Old Firm derby draw which means the Scottish title is now set to go to Celtic.
"We know what we need to do, we know how they play. We know how they played in Germany will be different at Ibrox."
If Leipzig and Frankfurt go through to the final in Seville on May 18, it will be the first all-German European final since Bayern Munich beat Dortmund at Wembley in the Champions League in 2013.
Meanwhile, Mourinho is hoping to win the first-ever edition of the Europa Conference League to add to the two Champions Leagues, UEFA Cup and Europa League he has won in his career.
His Roma side welcomes Leicester to the Stadio Olimpico following a 1-1 draw in England last week when Lorenzo Pellegrini's opener for the visitors was canceled out by a second-half own goal.
Roma may yet need to win the Conference League just to be in next season's Europa League given its stumbling form in recent weeks in Serie A, in which it is hanging on to the fifth place.
It is all about this competition now for a Leicester side sitting mid-table in the Premier League and dreaming of a first European final, and trophy, in Tirana on May 25.
"It is a really tough thing to come by, silverware. Some players never get the chance to win things," said Jonny Evans, who won the FA Cup with the Foxes last season.
in the other semifinal, Feyenoord heads to France to face Marseille defending a 3-2 lead from the first leg when Cyriel Dessers scored twice.
Europa League semifinals, second legs
Rangers (SCO) vs. RB Leipzig (GER) (0-1 agg)
Eintracht Frankfurt (GER) vs. West Ham United (ENG) (2-1 agg)
Europa Conference League semifinals, second legs
Roma (ITA) vs. Leicester City (ENG) (1-1 agg)
Marseille (FRA) vs. Feyenoord (NED) (2-3 agg)
