Arsene Wenger has made one change to the side that beat Manchester United 3-0 in the Premier League two weeks ago.
Laurent Koscielny returns to the starting line-up in place of Gabriel while Theo Walcott retains his position as striker.
Seven members of the starting XI have returned from international duty for the fixture at Vicarage Road.
Arsenal team to play Watford: Cech, Bellerin, Mertesacker, Koscielny, Monreal, Coquelin, Ramsey, Cazorla, Alexis, Ozil, Walcott
Arsenal subs: Macey, Debuchy, Gibbs, Arteta, Giroud, Oxlade-Chamberlain, Chambers
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