Manchester United have discovered the player Erik ten Hag's system revolves around

On a night filled with emotion and sadness, Manchester United produced a flat and disjointed performance that is unlikely to last long in the memory of anyone who attended.

United entered their Europa League group stage opener against Real Sociedad at Old Trafford with a spring in their step. The win over Arsenal on Sunday marked a fourth win on the bounce and Sociedad were next on their hit list.

However, perhaps impacted by the announcement of the death of Her Majesty, Queen Elizabeth II just 90 minutes before kick-off, United froze when they had the chance to build on their momentum. Brais Mendez's controversially-awarded penalty just short of the hour mark was enough to condemn United to their first defeat in five matches and inflict a rare Europa League home defeat.

READ MORE: United player ratings following Real Sociedad defeat

Although United had every right to complain about the awarding of the penalty, as the officials, despite the use of VAR being in operation, chose to ignore the fact the ball had hit substitute Lisandro Martinez's body before bouncing up onto his harm, the performance was flat. United were a far cry from the team that ended Arsenal's winning start to the season four days earlier.

But considering Erik ten Hag, in an attempt to mix things up and award minutes to those who have not been so fortunate recently, made six changes, it was always a decision that carried a degree of risk. It upset United's recent rhythm, with none of the sextet that came into the side doing enough to leave their calling card.

Casemiro, awarded his first start since arriving from Real Madrid last month, proved why Scott McTominay has kept his place in the last three league games, while Cristiano Ronaldo's most notable