Manchester United's caretaker boss Michael Carrick revealed the reason for the absence of England left back Luke Shaw against Villarreal.

Shaw suffered a head injury during the 4-1 loss to Watford in the Premier League, which led to the sacking of manager Ole Gunnar Solskjaer.

Given it was Shaw's second head injury in recent months, he was out of the squad per concussion protocols.

Alex Telles took his place for the game in Spain, which United won 2-0.

Carrick said to BT Sport: ''Luke had concussion a couple of weeks ago [during the Manchester derby against City] and then got another knock, so we just need to assess him as a precaution.''