The young Eagles will host the La Liga side at Sutton United’s VBS Community Stadium, with the tie to be played on or before Wednesday, 18th March.
Darren Powell's outfit progressed after topping Group B on nine points, level with both Valencia and Borussia Mönchengladbach. With the top two advancing, Palace secured qualification alongside Valencia courtesy of a superior goal difference.
That progression was sealed with a 2–0 victory over Borussia Mönchengladbach on Wednesday evening, as goals from Dylan Reid and Benji Casey ensured a crucial three points.
Real Sociedad B arrive in strong form, having topped Group C with 10 points from three wins and one draw.
Full fixture details – including broadcast and ticket information, as well as the confirmed date and kick-off time – will be announced in due course. Supporters will be updated as soon as they are confirmed.