Granit Xhaka will miss Arsenal's Europa League quarterfinal second-leg meeting with CSKA Moscow in Russia on Thursday.
The Switzerland midfielder has been left at home as he is suffering from flu.
Xhaka had started the first leg last week, a 4-1 win at the Emirates, as well as both games of the round-of-16 tie against AC Milan, in which he scored in the second leg.
That game marked an encouraging resurgence for the 25-year-old that continued on Sunday in the win against Southampton, after he struggled with form earlier in the season.
But he will not be available in Moscow, and Arsene Wenger could turn to Mohamed Elneny in midfield in Xhaka's place.
Henrikh Mkhitaryan has already been ruled out after suffering a knee injury in the first leg.