Arsenal boss Mikel Arteta is concerned about a muscular injury suffered by Viktor Gyokeres, with the Gunners working to discover the severity of the problem.
The Swedish forward missed training on Monday after being substituted with the issue during Saturday's 2-0 win over Burnley.
And the £64m did not travel for Arsenal's Champions League's trip to Slavia Prague on Tuesday.
Arteta said: 'He's definitely not available (for Slavia Prague). He hasn't trained today. We need to do some more tests and scans in the next few days to understand the extent of the injury.