Tall defender Stefan impressed for the under-21s last season, while also gaining welcome first-team experience during a brief loan spell at York City in League Two.
Usually a centre half, Stefan showed his versatility by filling in at right back, despite only playing five times for the Minstermen. The defender - who began his career as a winger - has already made his senior Arsenal bow, having come on against Galatasaray in the Champions League in 2014.
Stefan O'Connor Profile
January 23, 1997 Croydon
An England Under-17 international, Stefan is known for his physicality and ball-playing abilities, and has been at Arsenal since 2010 when he joined from the Crystal Palace academy.