Arsenal manager Mikel Arteta says teenage attacking midfielder Ethan Nwaneri will be "out for a few weeks" with a muscular issue.
The 17-year-old came off at half-time in Saturday's 1-1 draw at Brighton after scoring the game's opening goal.
The England Under-19s international made his first Premier League start three days earlier, during the Gunners' 3-1 win at Brentford.
"Unfortunately, he has picked up an injury and he is going to be out for a few weeks," said Arteta on Monday.
Nwaneri made his first-team breakthrough this season, with Saturday's goal his fifth in 18 appearances.