Ethan Nwaneri, 15, became the youngest player in Premier League history after coming on as a substitute in Arsenal's win against Brentford on Sunday.
Harvey Elliott had held the record, aged 16 years and 30 days when he played for Fulham in 2019.
"We have the opportunities to bring young players on," said Arsenal manager Mikel Arteta before the Brentford game.
He added: "We are pretty short and opportunities come when issues arise."
Nwaneri, who was born in March 2007, has been allocated the number 83 shirt.
He has already made a number of appearances for Arsenal at under-18s level and, aged 14, played for the England Under-16s.