Arsenal forward Kai Havertz is set for a spell on the sidelines after suffering a knee injury, sources have told ESPN.
The 26-year-old missed an open training session at Emirates Stadium on Wednesday but it is currently unclear how severe the issue is.
Sources say the club are waiting for the injury to settle down before undergoing further tests to determine the full extent of the problem.
Any lengthy spell out would be a significant blow to the Gunners, who are still without Gabriel Jesus for a prolonged period after undergoing knee surgery in January.
Havertz's absence would leave Arsenal with €63 million ($73m) summer signing Viktor Gyökeres as their only recognised centre-forward, although Leandro Trossard and Gabriel Martinelli have deputised in the position previously.
Arsenal are now set to weigh up their options whether to enter the market to replace Havertz. The Gunners hold an interest in Crystal Palace's Eberechi Eze but Tottenham Hotspur are in pole position to sign the attacking midfielder.
They were also admirers of Newcastle United's Alexander Isak -- now heavily linked with a big-money move to Liverpool -- prior to signing Gyokeres and need to balance their squad through departures after committing around £200m on new signings so far this summer.
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Havertz suffered a serious hamstring injury during the club's warm-weather training trip to Dubai in February but returned having noticeably added muscle to his physique after a rigorous recovery programme.
The Germany international played the final 30 minutes of Sunday's 1-0 win at Manchester United.
