A place in next month's showpiece event in Prague is up for grabs, with the victors of this contest to face either AZ Alkmaar or West Ham United.
Match preview
Basel were staring down the barrel of defeat, albeit a slender one, when they entered the closing stages of last week's first-leg tie with Fiorentina, with Arthur Cabral's 25th-minute opener against his former club putting the Italian side in control.
However, the Swiss outfit managed to complete a remarkable turnaround in the final 20 minutes courtesy of a stunning solo goal from Andy Diouf and a dramatic 92nd-minute winner from Zeki Amdouni - his sixth goal in as many matches in the competition.
FCB became the first team from Switzerland to win a semi-final tie in a major European competition since Grasshopper against Bastia in the 1977-78 UEFA Cup, and Heiko Vogel's side remain on course to become the first-ever Swiss club to reach a major European final.
Basel are still yet to lose against Fiorentina, winning two and drawing one of their three meetings and scoring twice on each occasion, and they can be confident of further success against the Italian side having progressed from all six major European knockout ties when winning the first leg away from home.
However, FCB enter Thursday's second leg after suffering a 6-1 defeat away against St Gallen in the Swiss Super League on Sunday - their heaviest defeat in any competition for nearly five years, albeit with a much-rotated side.
Success in the Europa Conference League appears to be Basel's strongest chance of qualifying for Europe next season as they currently sit sixth in the Super League table, four points behind Luzern in fourth with just three games remaining.
Fiorentina boss Vincenzo Italiano was left disappointed following last week's first-leg loss after his team failed to build on their dominant start before conceding two set-piece goals, but the 45-year-old is "convinced" that La Viola will take their chances in the second leg.
The Serie A side ended a three-game losing run when they secured a routine 2-0 home victory over Udinese on Sunday, with goals either side of half time from Gaetano Castrovilli and Giacomo Bonaventura helping the Florence-based outfit climb up to eighth in the table.
However, with hopes of securing a top-six finish in Serie A now mathematically over, winning the Europa Conference League is Fiorentina's only route into Europe for next season; not since lifting the European Cup Winners' Cup back in 1960-61 have La Viola had their hands on continental silverware.
Since failing to win their opening two ECL group-stage matches away from home, Italiano's men have comfortably won each of their last five games on the road, winning 3-0 against both Hearts and Rigas Futbola Skola before scoring four goals against Braga, Sivasspor and Lech Poznan in the knockout rounds.
Fiorentina have scored more goals (33) than any other team in this season's competition and they have also had plenty of joy in front of goal when visiting Basel, as they have scored at least two goals in each of their last five away meetings with the Swiss club, winning three times and drawing twice during this run.
However, La Viola have failed to progress from any of their previous six European knockout ties when losing the first leg, last doing so in the first round of the 1989-90 UEFA Cup when they came from one goal down to draw 1-1 with Atletico Madrid on aggregate before winning the tie on penalties.
Basel Europa Conference League form:
W
D
W
D
W
W
Basel form (all competitions):
L
W
W
L
W
L
Fiorentina Europa Conference League form:
W
W
W
W
L
L
Fiorentina form (all competitions):
D
W
D
L
L
W
Team News
Basel defender Arnau Comas has been sidelined since November with a long-term thigh injury and he is still unavailable for selection, but otherwise, Vogel has a fully-fit squad at his disposal.
Vogel made nine changes to the side that lost heavily against St Gallen on Sunday, resting the likes of goalkeeper Marwin Hitz and defensive duo Kasim Nuhu and Andy Pelmard who are all expected to be recalled to the first XI.
Dan Ndoye and former Roma youngster Riccardo Calafiori are set to start as wing-backs at the expense of Anton Kade and Liam Millar, while Diouf, Taulant Xhaka and Wouter Burger will likely operate in centre-midfield behind strikers Amdouni and Jean-Kevin Augustin.
As for Fiorentina, Cabral - who is the top scorer in the ECL this term with seven goals in 12 games - was rested last weekend having recently recovered from injury, but the Brazilian is expected to return to the starting lineup and join Jonathan Ikone and Nicolas Gonzalez in attack.
After also making nine changes to his starting lineup last time out, Italiano is set to recall a number of first-team regulars on Thursday, including goalkeeper Pietro Terracciano and right-back Dodo at the expense of Michele Cerofolini and Lorenzo Venuti respectively.
Bonaventura was shown a straight red card shortly after full time in La Viola's win over Udinese following a heated altercation with Rodrigo Becao, but the experienced midfielder is available for selection on Thursday and he is set start in the middle of the pitch alongside Sofyan Amrabat and Rolando Mandragora.
Basel possible starting lineup:
Hitz; Lang, Kasim, Pelmard; Ndoye, Xhaka, Burger, Diouf, Calafiori; Amdouni, Augustin
Fiorentina possible starting lineup:
Terracciano; Dodo, Milenkovic, Igor, Biraghi; Bonaventura, Amrabat, Mandragora; Ikone, Cabral, Gonzalez
We say: Basel 1-1 Fiorentina (Basel to win 3-2 on aggregate)
The onus is on Fiorentina to respond from their first-leg defeat with an improved performance in Thursday's reverse fixture, and the clinical prowess of former Basel man Cabral could be key in their quest to progress to the final.