Sub-plot: United have won eight, drawn nine and lost four in 21 meetings with Spanish opposition at Old Trafford in all European competitions.
Did you know? Real Sociedad abandoned their policy of only using players from the Basque region of Spain when they signed Republic of Ireland striker John Aldridge from Liverpool in 1989.
Rivals watch: Shaktar Donetsk, also unbeaten in this competition like United, will face Bayer Leverkusen in Germany at the same time, 19:45 BST, on Wednesday night.
More: Blackmore on Euro test | Moyes eyes Real Sociedad visit