In addition to the round-of-16 ties, to be played over two legs on 6 and 13 March, the entire path to the final in Bilbao is now mapped out for all of the teams remaining in the competition.
The away leg takes place first in San Sebastian, before La Real come to Old Trafford in the following week.
Real Socieded brushed Midtjylland aside in the play-offs to reach this stage.
United have faced Real Sociedad six times in competitive matches in our history.
In the 2013/14 Champions League, Inigo Martinez's early own goal was the difference at Old Trafford before a 0-0 draw in San Sebastian.