Arsene Wenger went with a back three for the first time in 20 years in Arsenal's last game, but the manager is likely to shift back to a back-four when the Gunners face Manchester City in the semifinals of the FA Cup at Wembley.
With Wenger still under pressure after another disappointing season, all Arsenal have to salvage is victory in the FA Cup. To do that, they must win this semifinal on Sunday, with the Frenchman needing his players, who have sometimes looked like they have stopped responding to their manager, to step up and play to their potential.
Wenger went with three central defenders in the game against Middlesbrough on Monday, and while Arsenal ended their poor away form with a 2-1 win, the Londoners didn't exactly look too comfortable in the formation.
Considering the importance of this game and the dangers that Manchester City possess in attack – Boro, the least creative team in the Premier League, were able to create a fair few chances against Arsenal – Wenger is expected to go back to the tried and tested.
Koscielny's usual partner – Shkodran Mustafi -- is still out through injury, along with Lucas Perez, Santi Cazorla, Jeff Reine-Adelaide and goalkeeper David Ospina. Danny Welbeck missed the Boro game, and is a doubt for the semifinal.
Manchester City could be boosted by the return of Gabriel Jesus, the pacy Brazilian, who made such a big impact after joining the club during the January transfer window.
Jesus has been out for a while after suffering a fracture in his foot, but has made a sooner-than-expected return and could feature in the matchday squad.
Centre-back John Stones is out with a muscle problem, while Ilkay Gundogan is a long-term absentee.
While Stones will be missed by Pep Guardiola, the manager will be happy with the return of the captain Vincent Kompany, who has come through well after playing in the Premier League last weekend, when he went on to score.
With Kompany at the back, Guardiola will hope City defend a whole lot better than they did the last time they played Arsenal, earlier this month, which ended in a 2-2 draw.
Expected starting XI:
Arsenal: Petr Cech; Hector Bellerin, Laurent Koscielny, Gabriel, Nacho Monreal; Granit Xhaka, Aaron Ramsey; Alex Oxlade-Chamberlain, Mesut Ozil, Alexis Sanchez; Olivier Giroud.
Manchester City: Willy Caballero; Jesus Navas, Vincent Kompany, Nicolas Otamendi, Gael Clichy; Fernandinho, Toure; De Bruyne, Silva, Sane; Aguero.