Manchester United manager David Moyes questioned the referee's performance following their draw in San Sebastian.
Marouane Fellaini was sent off late on for a second bookable offence, after Robin van Persie missed a penalty for United, following a dive by Ashley Young.
"I thought there were some strange decisions all night, and that was another one," Moyes told ITV's Gabriel Clarke afterwards.
"I think throughout the night there were a few things I found odd. I think it was the totting up that cost him [Fellaini] in the end."
The Scot spoke positively about his team's performance in northern Spain, as they took a point away from the Anoeta.
"We had chances to win, especially second half - we controlled most of, but for one or two moments, we were on top."