The striker came off the bench for the ineffectual Wayne Rooney as David Moyes' side let the chance to take control of their Champions Leage group slip in Spain
Robin van Persie missed a penalty and Marourane Fellaini was sent off as United saw their four-game winless run away from home in the Champions League continue.
The point was Real Sociedad's first of this season's competition and keeps their slim hopes of qualifying for the knockout stages alive given Bayer Leverkusen and Shakhtar Donetsk also drew.
|By Sam Lee
A draw away from home in the Champions League can never be sniffed at, but Manchester United will go away from Anoeta thinking they could have taken all three points to all but seal qualification to the last 16.
Robin van Persie showed more hints at this season's toil by hitting the post twice, once with the goal gaping and then from the penalty spot, while Ashley Young endeared himself to nobody with another dive and poor performance.
Things never quite clicked for David Moyes' men, with Chicharito blazing over the crossbar with the goal at his mercy. It could've been worse, though, had the hosts taken their chances.
All in all, Moyes will be pleased to have the opportunity to qualify for the knockout stages in Leverkusen next time out, but the hard work could've been done and dusted in the Basque country on Tuesday.
The hosts made four changes from their 5-0 victory over Osasuna on Saturday as Markel Bergara, Alberto de la Bella, Mikel Gonzalez and Imanol Agirretxe all started having been on the bench at the weekend.
David Moyes opted to field Hernandez up front with Wayne Rooney as opposed to Van Persie, the Dutchman named among the substitutes. Hernandez was one of six changes for United from their victory over Fulham in the Premier League.
The visitors started confidently and pressed Sociedad high up the pitch, creating the first chance of the match in the 10th minute.
Shinji Kagawa released Patrice Evra down the left-hand side, the Frenchman found Rooney inside the penalty area and he flicked the ball back to the Japan international to fire a deflected shot wide.
It took the best part of half an hour for Sociedad to create an opening that came after David Zurutuza broke down the right.
The midfielder pulled his cross back to Agirretxe on the penalty spot, but he skewed his effort well wide of David de Gea’s goal.
United should have taken the lead early in the second half, but Hernandez was guilty of missing an open goal in the 50th minute.
Kagawa shifted the ball past Carlos Martinez and delivered a low cross into the unmarked Mexican, but he ballooned his effort over the bar from six yards.
The visitors’ frustration continued just after the hour as Van Persie – introduced in place of Rooney – struck the post with his first touch after an excellent cross from fellow substitute Ashley Young.
The Netherlands international striker was given another opportunity to score four minutes later after Bergara was adjudged to have pulled back Young inside the penalty area.
Van Persie’s spot-kick beat Claudio Bravo but struck the post and was cleared to safety by the Sociedad defence.
Fellaini spoiled United's night with his late dismissal after a second yellow card following a challenge on Zurutuza.