Former Premier League official Dermot Gallagher has acknowledged that Chelsea conceded their first goal against Manchester United in "unfortunate" circumstances.

Shortly after Willian had put Chelsea in front, Romelu Lukaku fired home from close range but only after the Belgian had got back to his feet after clashing heads with Andreas Christensen.

The incident left Christensen out of position and behind play as he got to his feet, but Gallagher has claimed that referee Martin Atkinson made the correct decision in allowing the action to continue.

Gallagher told Sky Sports News: "I think this proves that football isn't an exact science and refereeing certainly isn't.

"If a player is down and a referee thinks that he has got a head injury, he will stop play. In that incident, I think the two players clashed heads, the ball is knocked away and Christensen went down quickly. He then chose to get up quickly but by the time that Martin Atkinson has looked around, he is already getting up and that sells in the referee's mind that he hasn't got a head injury.

"He may well have but in Martin's eyes, the fact that the player has got up will tell him that he hasn't. He then carries on and I admit - he is out of position - which is unfortunate. The referee is duty bound to let the game carry on."

United would go on to secure a 2-1 victory at Old Trafford thanks to Jesse Lingard's second-half header.