The Turkish giants produced the performance of last week's first legs as they ran out 3-0 victors in Belgium, putting them on the brink of a last-eight spot.
Match preview
Being involved in a fierce two-horse race with Galatasaray for the Super Lig title means that Fenerbahce's priority is certainly on dethroning their rivals and last year's champions.
Just two points separate teams that have lost only once in 29 league fixtures during 2023-24, while Fenerbahce travel to third-placed Trabzonspor on Sunday.
Nevertheless, Ismail Kartal and his players know that there is an opportunity to win a recognised European competition for the first time in their history, their previous best effort being a Europa League semi-final in 2012-13.
Scoring twice during the latter stages of the first leg of this last-16 tie could prove pivotal, Dusan Tadic's last-gasp penalty further extending the margin of victory to 3-0.
Fenerbahce are aware that it is not necessarily an unassailable lead - they lost 3-0 to Ankaragucu in the Turkish Cup last month - but that represents their only defeat in any game since the start of December.
Having defeated Eintracht Frankfurt in the previous round, Union SG would have felt extremely hard-done-by to be drawn against Fenerbahce at this stage.
However, they can have few complaints of being in this predicament when they were within six minutes plus added-on time of travelling to Turkey trailing by just the one goal.
The Jupiler League leaders responded to a certain extent three days later by earning a 1-1 draw at home to Gent, still holding a six-point lead in top spot.
In terms of scoring three goals in a match, though, Alexander Blessin's side have achieved that feat just twice in 15 matches since the turn of the year.
Fenerbahce Europa Conference League form:
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W
Fenerbahce form (all competitions):
D
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Union SG Europa Conference League form:
D
W
L
Union SG form (all competitions):
W
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D
Team News
Kartal must find a balance when it comes to selecting his starting lineup, yet his team may not be too dissimilar from the one that featured in the first leg.
The likes of Bright Osayi-Samuel, Alexander Djiku, Ismail Yuksek, Sebastian Szymanski and Michy Batshuayi could all be recalled after dropping to the substitutes' bench at the weekend.
Dusan Tadic may also be rested, giving Ryan Kent the chance to make a rare start on the left flank.
With Christian Burgess having collected three yellow cards in European games this season, Alessio Castro-Montes may drop into the back three and an alternative being deployed at right-wing back.
Casper Terho could be used in that role, while Dennis Eckert Ayensa may be recalled in attack at the expense of Mohamed Amoura.
Fenerbahce possible starting lineup:
Livakovic; Osayi-Samuel, Dijku, Soyuncu, Oosterwolde; Fred, Yuksek; Under, Szymanski, Kent; Batshuayi
Union SG possible starting lineup:
Moris; Castro-Montes, Sykes, Machida; Terho, Sadiki, Puertas, Vanhoutte, Teklab; Ayensa, Nilsson
We say: Fenerbahce 1-2 Union SG (Fenerbahce to win 4-2 on aggregate)
With Union SG needing to throw caution to the wind to get back into this contest, we expect the visitors to get on the scoresheet in Turkey. Nevertheless, Fenerbahce have the experience to negotiate this game, even if it ends up in a narrow defeat.