Van Persie misses out for Man United
Manchester United's Scottish manager David Moyes (L) speaks to Dutch striker Robin van Persie during a training session in Manchester, Northwest England, on October 22, 2014
He completed the full 90 minutes in United's 1-1 draw at home to Southampton on Saturday, but was not even named in the squad for the visit of the Basque side.
Javier Hernandez took Van Persie's place at the tip of the United attack, in one of four changes to the team held by Southampton.
Real Sociedad, meanwhile, restored captain Xabi Prieto to the starting XI after he made his comeback following a lay-off with a hamstring injury in the weekend victory at Valencia.
United top the group with four points from their opening two games, while Real Sociedad have yet to pick up a point in this season's competition.