Both national champions, the two sides played out an entertaining first leg, in which a late penalty earned the Swiss side a precious lead to take to Turkey.
Match preview
Meeting for the first leg of their Champions League playoff last week, Galatasaray and Young Boys engaged in a battle royale at Wankdorf Stadium, which witnessed an absorbing contest that leaves the tie finely poised.
After trailing by two goals at the break, Gala flipped the script when substitute Michy Batshuayi struck twice shortly after leaving the bench - the first coming from his very first touch.
However, when Abdulkerim Bardakci handled the ball - an offence for which he was shown a second yellow card - Filip Ugrinic fired home a late penalty to earn a 3-2 win for the reigning Swiss champions.
Having narrowly failed to hang on for a draw, Galatasaray have now lost their last four European away matches - after going unbeaten through the previous 10 - and they return to Turkey with a deficit to make up.
Okan Buruk's men pipped arch-rivals Fenerbahce to the Super Lig title last season, posting a record tally of 102 points in the process, but they suffered a 5-0 thrashing by Besiktas in the recent Turkish Super Cup.
They then required two late goals to win their first league fixture at home to Hatayspor, before going on to beat Konyaspor 2-1; and following first-leg defeat in Bern, their hopes of reaching the Champions League group phase now hang by a thread.
Although they will have a lead to preserve on Tuesday night, thanks to that late Ugrinic spot-kick and two Joel Monteiro goals at either end of the first half, Young Boys might have been within touching distance of effectively wrapping up qualification.
Speedy winger Ebrima Colley hit the post before Batshuayi intervened, and what could have been a 3-0 lead then evaporated, as YB's defensive woes continued.
The Swiss champions are still searching for their first Super League win after five matches, having gone into the new season aiming to extend their dominance: three straight defeats left them rock bottom, before successive 2-2 draws belatedly got some points on the board.
Including Batshuayi's brace, new boss Patrick Rahmen has seen his side concede 15 goals so far, but making it into the Champions League group stage - as Young Boys did last year - would certainly ease the pressure.
Former coach Raphael Wicky led YB to third place behind Manchester City, RB Leipzig and Red Star Belgrade, before they went on to lose in the Europa League knockout-round playoffs.
Now, finishing the job against Gala - who also had the weekend off from domestic action - would secure eight money-spinning fixtures between September and January, allowing the Bern club to keep hold of their key players.
Galatasaray Champions League form:
L
Galatasaray form (all competitions):
Young Boys Champions League form:
W
Young Boys form (all competitions):
L
L
L
D
D
W
Team News
As Abdulkerim Bardakci is banned due to his sending-off in the first leg, Gala coach Okan Buruk must make at least one change to his starting XI.
Furthermore, captain and first-choice goalkeeper Fernando Muslera came off injured last week, so Gunay Guvenc may be required to deputise, while Kaan Ayhan returns from suspension just in time to feature in defence.
Davinson Sanchez has been sidelined by injury, and the Colombian centre-back joins experienced winger Wilfried Zaha in being strongly linked with a move away from Istanbul before the transfer window slides shut.
Despite his heroics in Bern, Michy Batshuayi is set to start on the bench, as Mauro Icardi again leads the line, having racked up 32 goals and 12 assists across all competitions last season.
Young Boys, meanwhile, will be unable to call upon Facinet Conte and Saidy Janko, but Kastriot Imeri has now recovered from an ankle injury.
Like Gala, YB lost their goalkeeper during last week's match, as injury victim David Von Ballmoos was replaced by Marcel Keller; the 22-year-old may have to stand in again on Tuesday.
Galatasaray possible starting lineup:
Muslera; Jelert, Nelsson, Ayhan, Kohn; Torreira, Sara; Yilmaz, Mertens, Akturkoglu; Icardi
Young Boys possible starting lineup:
Keller; Blum, Camara, Zoukrou, Hadjam; Lauper, Niasse; Monteiro, Ugrinic, Colley; Ganvoula
We say: Galatasaray 2-1 Young Boys (4-4 on aggregate; Galatasaray win on penalties)
The two teams were well matched in Switzerland, and given both sides' defensive issues, there could be plenty of goalmouth action throughout this second leg.