The home side seeks promotion to the top flight, while the visitors need a win to retain their Super League status.
Match preview
Grasshoppers hosted the first leg at Letzigrund Stadium last Sunday, only managing a 1-1 draw thanks to a late penalty.
Marco Schallibaum's side fell behind in the 52nd minute to a Marc Gutbub goal for Thun. The game seemed destined for defeat for Grasshoppers, but Giotto Morandi stepped up in the 97th minute to convert a penalty, leaving the tie level heading into the second leg.
The Zurich-based side have struggled throughout the season, finishing in the relegation playoff zone with 38 points from 38 matches. This is the first time they will be at risk of relegation since their promotion in the 2020-21 season.
To avoid the drop, Grasshoppers need their first win against Thun since 2021. They must also find a way to end their ten-game winless run away from home, having last won an away fixture in December.
Thun had a stellar regular season in the Swiss second division, amassing 76 points from 36 matches, finishing second, just three points behind the top spot.
Following relegation from the Super League in the 2019-20 season, the side from Bernese Oberland have endured four seasons in the lower division, never finishing first for automatic promotion.
The hosts are no strangers to the playoffs, having participated three times in the last five seasons. Their first attempt came in the 2019-20 season, where they fought to remain in the top flight but lost to second-division FC Vaduz and were relegated.
The following season (2020-21), Thun found themselves back in the playoffs as runners-up in the Swiss second division, but they were defeated again, this time by FC Sion.
Thun will hope that the third time's the charm, playing at home in the crucial second leg on Friday. They are unbeaten in their last three meetings against Grasshoppers, recording two wins and a draw.
Mauro Lustrinelli's side are also currently on a ten-match winning streak on home soil and will hope for fervent home support once again to push them towards victory.
Thun form (all competitions):
Grasshopper Zurich Swiss Super League form:
L
W
D
W
L
D
Team News
Thun will remain without 22-year-old centre-forward Hermann Tebily, and centre-back Erik Wyssen for this clash.
Gutbub found the net in the first leg and he will be looking to repeat this feat when he starts in attack alongside Koro Kone on Friday.
Grasshoppers will be without Meritan Shabani and Michael Kempter, who are both out of the season due to anterior cruciate ligament injuries.
Twenty-year-old midfielder Dijon Kameri is also sidelined with a muscle injury until later next month.
Tsiy-William Ndenge, Francis Momoh and Morandi are three players to watch out for in the away side.
Thun possible starting lineup:
Hammel; Abels, Tobersi, Seko, Ndicka; Abrashi, Ndenge; Momoh, Morandi, Mabil; Abubakar
Grasshopper Zurich possible starting lineup:
Matic; Dahler, Sutter, Burki, Franke; Bertone, Janjicic, Roth; Santos; Gutbub, Kone
We say: Thun 1-0 Grasshopper Zurich
Thun have dominated teams on home soil and this might likely help them get over the line in this one. The away side have also struggled on the road and in recent meetings against the hosts, leaving us to predict a slender win for the home side.