Arsenal boss Unai Emery says Dani Ceballos has what looks like a "small" hamstring injury sustained in the Europa League draw with Vitoria SC.
The midfielder initially pulled up early in the second half of the 1-1 result in Guimaraes and was replaced by Matteo Guendouzi 54 minutes in.
The Real Madrid loanee appears likely to miss at least Saturday's Premier League trip to Leicester City, although Emery says he will have further tests on Thursday.
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"We are going to wait for the analysis tomorrow but, at the beginning, I think it’s a small injury," Emery told a news conference.