Arsenal suffered a further midfield setback against Watford as Aaron Ramsey departed the match after just 20 minutes with an apparent calf injury.
The night started badly for both Ramsey and Arsenal as the Wales international deflected a Younes Kaboul header past Petr Cech to hand Watford a surprise lead after 10 minutes at Emirates Stadium.
Things got worse for the Gunners as Watford seized on a lapse in concentration three minutes as Etienne Capoue waltzed through the hosts' defence and forcing Cech into a save, with Troy Deeney finishing the follow-up.
Ramsey soon hit the floor in frustration and needed treatment as he signalled to his calf, and Wenger - serving the second game of his four-match touchline ban - was forced to bring on Alex Oxlade-Chamberlain to partner Francis Coquelin in midfield.
In Pictures | Arsenal vs Watford | 31/01/2017
Any significant injury layoff for Ramsey would be a huge setback for Arsenal ahead of this weekend's clash against Chelsea, with Santi Cazorla out with a long-term achilles problem, Mohamed Elneny at the African Cup of Nations, and Granit Xhaka still serving a suspension.
