The former Gunners winger impressed while in charge of the U23s last season.
Ljungberg has now joined Unai Emery's staff in a role that will help bridge the gap between the U23s and first-team.
Speaking on the Arsenal website, Sanllehi said: "Identifying, recruiting and developing young players is a key part of our strategy.
"We have some great talent coming through our younger age groups and, like all top clubs, the challenge is to help them make the most of their abilities.
"The hardest part is always the transition from academy football to senior football. We already have good programmes in place but these staff changes will ensure our plans are even more robust and clear for every single player.
"I'm confident it will make a significant difference to our ability to bring players through to the first team."